Wiring boards for array-based electronic devices

ABSTRACT

In accordance with certain embodiments, lighting systems include one or more lightsheets each including a plurality of strings of light-emitting elements, control elements, and power conductors for supplying power to the light-emitting elements and control elements.

RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 13/799,807, filed Mar. 13, 2013, which claims the benefit ofand priority to U.S. Provisional Patent Application No. 61/697,411,filed Sep. 6, 2012, the entire disclosure of each of which is herebyincorporated herein by reference.

FIELD OF THE INVENTION

In various embodiments, the present invention generally relates toelectronic devices, and more specifically to array-based electronicdevices.

BACKGROUND

Light sources such as light-emitting diodes (LEDs) are an attractivealternative to incandescent and fluorescent light bulbs in illuminationdevices due to their higher efficiency, smaller form factor, longerlifetime, and enhanced mechanical robustness. Broad-area lightingsystems such as those designed to replace fluorescent tubes mustuniformly distribute the light over the emitting aperture of thelighting system. In some cases, relatively high-power LEDs are utilizedin such lighting systems, but use of such LEDs typically requiresadditional optics or mixing chambers to spread out and/or diffuse thelight, which add cost and bulk and reduce efficiency.

LED-based lighting systems based on relatively large arrays ofrelatively low-power LEDs may be used as an alternative to the use ofsmaller numbers of high-power LEDs. Such systems may use packaged orunpackaged LEDs. Some systems may be formed using a low cost plasticsubstrate, while others may utilize more conventional printed circuit orwiring boards, such as FR4 or metal core printed circuit board (MCPCB).These systems may feature conductive traces formed over a low-costplastic substrate (e.g., a plastic wiring board) interconnecting a largearray of packaged or unpackaged LEDs. Such systems have been describedin U.S. patent application Ser. No. 13/171,973, the entire disclosure ofwhich is incorporated herein by reference.

One potential limitation of such systems is that once the pattern isformed on the circuit board or substrate, the size of the printed areaand the pitch and layout of LEDs generally cannot be changed. This is aparticular limitation when utilizing high-volume manufacturing, such asroll-to-roll processing, where very large amounts of a single design orlayout of a printed sheet must be processed to achieve sufficiently lowcost. Thus, supporting a large number of different products havingdifferent printed sheet configurations typically requires a large numberof printed sheets in inventory and a correspondingly highermanufacturing cost.

A second limitation arises from the electrical topography used in suchsystems, which typically features large numbers of strings ofseries-connected LEDs. Because of inherent variations in the forwardvoltage of the LEDs, as well as potential variations in the resistanceof the conductive traces, one generally cannot simply connect all of thestrings in parallel and expect that the current will divide equally orsubstantially equally among the strings. In such a system, one stringmay have a relatively lower string voltage, and thus a higher currentwill flow through the string. As more current flows through the string,the LEDs in that string will heat up, causing the LED forward voltage todecrease, resulting in a further increase in current. This results in“current-hogging” in the relatively lower-voltage strings and may resultin failure of one or more LEDs in a string, which may cascade intofailure of the lighting system.

Conventional LED systems utilize a constant-current driver that providesa constant current to a series-connected string of LEDs, independent ofthe string voltage. While such an approach works for conventional LEDsystems, array-based lighting systems may have tens or hundreds ofstrings of LEDs. Using a separate constant current driver for eachstring in this situation may be prohibitively expensive. Furthermore,the number of connection points to each sheet in such a scenario isgenerally roughly equal to the number of strings. Again, this is verycostly and potentially is a source of failures that may decreasereliability. Furthermore, providing for such a large number ofconnections requires a relatively large amount of space or volume,making such systems difficult to install and manage.

A third limitation is related to the fabrication of larger lightingsystems by tiling multiple discrete lighting units together. In additionto the cost of assembling such a system, there is often an undesirablelower light intensity, a dark space, or a different color light in theregion surrounding the joints between different lighting units. Such anundesirable characteristic at the joint may, for example, be a result ofthe need to provide additional space between different lighting units toaccommodate means for mechanically supporting the lighting units,physically connecting the lighting units, electrically connecting thelighting units, and/or connecting the lighting units to the powersource.

In view of the foregoing, a need exists for systems and techniquesenabling the low-cost design and manufacture of reliable array-basedlighting systems capable of supporting a large number of differentproducts and having a cost-effective drive and interconnect system, aswell as the ability to make uniform and reliable large-area lightingsystems at low cost.

SUMMARY

In accordance with certain embodiments, lighting systems are fabricatedutilizing discrete lightsheets that may be tiled (i.e., joined alongfacing edges) in one or more directions. Such lightsheets typicallyinclude multiple strings of series-connected light-emitting elements(LEEs) and a control element electrically connected to each string.Advantageously, the pitch between strings and/or LEEs may be constantacross single lightsheets or even across multiple joined (i.e., tiled)lightsheets, notwithstanding the joints between the lightsheets. Thus,lighting systems in accordance with embodiments of the present inventionmay have substantially arbitrary sizes but have a consistent appearance(e.g., luminance of emitted light) across their entire areas. Thecontrol elements may thus be present on the lightsheets within orbetween strings of LEEs so as not to interrupt the LEE pitch. Similarly,larger lightsheets may be segmented into smaller lightsheets (e.g., byseparation between two strings of LEEs) while still maintaining fullfunctionality of each smaller segment. Power may be supplied to the LEEsvia power conductors located on, e.g., one or more edges or sides of thelightsheets, and the resistance of such conductors may be advantageouslydecreased via connection to larger conductive areas located on the back(i.e., the non-light-emitting side) of the lightsheets.

In some embodiments, various elements such as substrates or lightsheetsare “flexible” in the sense of being pliant in response to a force andresilient, i.e., tending to elastically resume an original configurationupon removal of the force. Such elements may have a radius of curvatureof about 50 cm or less, or about 20 cm or less, or about 5 cm or less,or even about 1 cm or less. In some embodiments, flexible elements havea Young's Modulus less than about 50×10⁹ N/m², less than about 10×10⁹N/m², or even less than about 5×10⁹ N/m². In some embodiments, flexibleelements have a Shore A hardness value less than about 100; a Shore Dhardness less than about 100; and/or a Rockwell hardness less than about150.

In an aspect, embodiments of the invention feature a lighting systemincluding or consisting essentially of a substantially planarlightsheet, first and second spaced-apart power conductors eachextending in a first direction and disposed on the lightsheet, aplurality of light-emitting strings, and a plurality of controlelements. Each light-emitting string (i) includes or consistsessentially of a plurality of interconnected light-emitting elementsspaced along the light-emitting string, (ii) has a first endelectrically coupled to the first power conductor, (iii) has a secondend electrically coupled to the second power conductor, and (iv) isoriented in a second direction not parallel to the first direction. Thepower conductors supply power to each of the light-emitting strings.Each control element is (i) electrically connected to at least onelight-emitting string and (ii) configured to utilize power supplied fromthe power conductors to control power (e.g., supply a substantiallyconstant current) to the light-emitting string(s) to which it iselectrically connected. The lightsheet is separable, via a cut (i.e.,any physical break or separation, not necessarily made by cutting)spanning the first and second power conductors and not crossing alight-emitting string, into two partial lightsheets each including orconsisting essentially of (i) one or more light-emitting strings, (ii)one or more control elements, and (iii) portions of the first and secondpower conductors configured to supply power to and thereby illuminatethe one or more light-emitting strings of the partial lightsheet.

Embodiments of the invention may include one or more of the following inany of a variety of different combinations. A power supply may beelectrically connected to the power conductors and configured to providea substantially constant voltage to the power conductors. A secondlightsheet may be coupled to the lightsheet. The second lightsheet mayinclude third and fourth spaced-apart power conductors disposed thereon,and the power supply may be configured to supply a substantiallyconstant voltage to the third and fourth power conductors. Eachlight-emitting string may include or consist essentially of only 12, 16,18, or 20 light-emitting elements. The constant voltage provided to thepower conductors does not exceed approximately 60 volts. None of thelight-emitting strings may extend beyond an area spanned by the firstand second power conductors. None of the light-emitting strings mayintersect another light-emitting string. The second direction may besubstantially perpendicular to the first direction. For eachlight-emitting string, the light-emitting elements thereof may be spacedapart along the light-emitting string at a substantially constantlight-emitting-element pitch. The light-emitting strings may be spacedapart on the lightsheet at a substantially constant string pitch. Thestring pitch may be an integer multiple of the light-emitting-elementpitch, where the integer is greater than 1. The string pitch may beapproximately equal to the light-emitting-element pitch. The lightsheetmay be separable into the two partial lightsheets via a cut between anytwo light-emitting strings on the lightsheet. The lightsheet may beseparable into more than two partial lightsheets.

Over the lightsheet, light-emitting elements may be spaced apart at asubstantially constant light-emitting-element pitch maintained betweenlight-emitting elements of different light-emitting strings. Eachcontrol element may be electrically connected to a differentlight-emitting string. For each light-emitting string, light-emittingelements thereof may be spaced apart at a substantially constantlight-emitting-element pitch independent of a position of the controlelement electrically connected to the light-emitting string. Eachlight-emitting string may include or consist essentially of only 12, 16,18, or 20 light-emitting elements. Each light-emitting string mayinclude or consist essentially of only 60, 72, 84, 90, 96, 108, 126,140, 150, 156, 160, 198, 200, 204, or 211 light-emitting elements. Eachlight-emitting string may include or consist essentially of only 120,144, 168, 180, 210, or 216 light-emitting elements. Light-emittingelements of each light-emitting string may be connected in series. Atleast one control element may be configured to provide a substantiallyconstant current to the at least one light-emitting string to which thecontrol element is connected. At least one light-emitting element mayemit substantially white light. At least one light-emitting element mayinclude or consist essentially of a bare-die light-emitting diode or apackaged light-emitting diode. At least one light-emitting string may bea folded string having a straight-line length (i.e., the length of thestring if all of the light-emitting elements were connected along asingle straight line) longer than a dimension of the lightsheet spannedby the power conductors. The lightsheet may include a substrate on whichthe plurality of light-emitting strings is disposed. Each light-emittingstring may include a plurality of conductive elements, disposed over thesubstrate, electrically connecting the plurality of light-emittingelements and the control element. A conductive adhesive, an anisotropicconductive adhesive, a wire bond, and/or solder may electrically connectthe light-emitting elements to the conductive elements. The lightsheetmay be flexible.

In another aspect, embodiments of the invention feature a lightingsystem including or consisting essentially of a substantially planarlightsheet, disposed on the lightsheet, first and second spaced-apartpower conductors each extending in a first direction, a plurality oflight-emitting strings, and a plurality of control elements. Each lightemitting string (i) comprises a plurality of interconnectedlight-emitting elements spaced along the light-emitting string, (ii) hasa first end electrically coupled to the first power conductor, (iii) hasa second end electrically coupled to the second power conductor, and(iv) is oriented in a second direction not parallel to the firstdirection. The power conductors supply power to each of thelight-emitting strings. Each control element is (i) electricallyconnected to at least one light-emitting string and (ii) configured toutilize power supplied from the power conductors to control the currentto the at least one light-emitting string to which it is electricallyconnected. For each light-emitting string, a pitch at which thelight-emitting elements are spaced is independent of a position of thecontrol element electrically connected to the light-emitting string.

Embodiments of the invention may include one or more of the following inany of a variety of different combinations. The lightsheet may beseparable, via a cut spanning the first and second power conductors andnot crossing a light-emitting string, into two partial lightsheets eachincluding or consisting essentially of (i) one or more light-emittingstrings, (ii) one or more control elements, and (iii) portions of thefirst and second power conductors configured to supply power to andthereby illuminate the one or more light-emitting strings of the partiallightsheet. A power supply configured to provide a substantiallyconstant voltage to the power conductors may be electrically connectedto the power conductors. A second lightsheet may be coupled to thelightsheet and include third and fourth spaced-apart power conductorsdisposed thereon. The power supply may be configured to supply thesubstantially constant voltage to the third and fourth power conductors.Each light-emitting string may include or consist essentially of only12, 16, 18, or 20 light-emitting elements. The substantially constantvoltage provided to the first and second (and even the third and fourth)power conductors may not exceed approximately 60 volts. The power supplymay be configured to adjust a light output of the lightsheet bypulse-width-modulating the substantially constant voltage. None of thelight-emitting strings may extend beyond an area spanned by the firstand second power conductors. None of the light-emitting strings mayintersect another light-emitting string. The second direction may besubstantially perpendicular to the first direction. For eachlight-emitting string, the light-emitting elements thereof may be spacedapart along the light-emitting string at a substantially constantlight-emitting-element pitch. The light-emitting strings may be spacedapart on the lightsheet at a substantially constant string pitch. Thestring pitch may be an integer multiple of the light-emitting-elementpitch, where the integer is greater than 1. The string pitch may beapproximately equal to the light-emitting-element pitch. Over thelightsheet, light-emitting elements may be spaced apart at asubstantially constant light-emitting-element pitch maintained betweenlight-emitting elements of different light-emitting strings. Eachcontrol element may be electrically connected to a differentlight-emitting string. For each light-emitting string, light-emittingelements thereof may be spaced apart at a substantially constantlight-emitting-element pitch independent of a position of the controlelement electrically connected to the light-emitting string.

Each light-emitting string may include or consist essentially of only12, 16, 18, or 20 light-emitting elements. Each light-emitting stringmay include or consist essentially of only 60, 72, 84, 90, 96, 108, 126,140, 150, 156, 160, 198, 200, 204, or 211 light-emitting elements. Eachlight-emitting string may include or consist essentially of only 120,144, 168, 180, 210, or 216 light-emitting elements. Light-emittingelements of each light-emitting string may be connected in series. Atleast one control element may be configured to provide a substantiallyconstant current to the at least one light-emitting string to which thecontrol element is connected. At least one light-emitting element mayemit substantially white light. At least one light-emitting element mayinclude or consist essentially of a bare-die light-emitting diode or apackaged light-emitting diode. At least one light-emitting string may bea folded string having a straight-line length longer than a dimension ofthe lightsheet spanned by the power conductors. The light-emittingelements of the folded string may have a positive terminal and anegative terminal, and all of the positive terminals may be orientedtoward a single edge of the lightsheet notwithstanding folds in thefolded string. The lightsheet may include a substrate on which theplurality of light-emitting strings is disposed and each light-emittingstring may include a plurality of conductive elements, disposed over thesubstrate, electrically connecting the plurality of light-emittingelements and at least one the control element. A conductive adhesive, ananisotropic conductive adhesive, a wire bond, and/or solder mayelectrically connect the light-emitting elements to the conductiveelements. The substrate may include or consist essentially ofpolyethylene terephthalate, polyethylene naphthalate, polycarbonate,polyethersulfone, polyester, polyimide, polyethylene, fiberglass, metalcore printed circuit board, and/or paper. The conductive elements mayinclude or consist essentially of aluminum, chromium, copper, gold,carbon, silver, carbon ink, and/or silver ink. An insulating layer maybe disposed over at least portions of some of the conductive elements.The insulating layer may include or consist essentially of an insulatingink.

The lightsheet may be flexible. At least one control element may includeor consist essentially of a plurality of active and/or passive circuitelements. At least one control element may include or consistessentially of (i) one or more resistors and/or (ii) one or moretransistors. At least one control element may include or consistessentially of an integrated circuit, e.g., a packaged integratedcircuit or a bare-die integrated circuit. Each control element may beelectrically connected to only one light-emitting string. The system mayinclude one or more additional lightsheets each having a tilingdirection, and the lightsheet and the one or more additional lightsheetsmay be connected to each other in the tiling direction at interfacestherebetween. A pitch of light-emitting elements may be substantiallyconstant across the lightsheet and the one or more additionallightsheets notwithstanding the interfaces. The lightsheet and the oneor more additional lightsheets may be electrically connected in seriesor in parallel. Each control element may be electrically connected to adifferent light-emitting string, and a voltage across each of theplurality of light-emitting strings may be at least equal to a sum of avoltage drop across the plurality of light-emitting elements in onestring and a voltage drop across the control element electricallyconnected to the one string. At least one control element may beconfigured to control an optical characteristic of the light-emittingelements of the at least one string to which it is electricallyconnected. The optical characteristic may include or consist essentiallyof chromaticity, color temperature, intensity, color rendering index,spectral power distribution, and/or spatial light distribution pattern.At least one control element may be configured to control the opticalcharacteristic by selectively de-energizing various ones of thelight-emitting strings, thereby dimming a light output from thelightsheet, without altering a drive current supplied to the remaininglight-emitting strings. At least one first light-emitting string mayemit light having a chromaticity, color temperature, intensity,efficiency, color rendering index, or spectral light distributiondifferent from a chromaticity, color temperature, intensity, efficiency,color rendering index, spectral power distribution, or spatial lightdistribution of at least one second light-emitting string.

The plurality of light-emitting strings may include or consistessentially of (i) a first group of one or more light-emitting stringsand (ii) a second group of one or more light-emitting strings differentfrom the first group. The at least one control element may be configuredto control the optical characteristic by activating the first group anddeactivating the second group to produce light having a firstchromaticity, color temperature, intensity, efficiency, color renderingindex, spectral power distribution, or spatial light distribution, andactivating the second group and deactivating the first group to producelight having a second chromaticity, color temperature, intensity,efficiency, color rendering index, spectral power distribution, orspatial light distribution different from the first chromaticity, colortemperature, intensity, efficiency, color rendering index, spectralpower distribution, or spatial light distribution. The plurality oflight-emitting strings may include or consist essentially of a firstgroup of one or more light-emitting strings and, associated with atleast one of the light-emitting elements of the first group, a firstoptical element of a first type. The plurality of light-emitting stringsmay include or consist essentially of a second group, different from thefirst group, of one or more light-emitting strings and, associated withat least one of the light-emitting elements of the second group, asecond optical element of a second type different from the first type.The at least one control element may be configured to control theoptical characteristic by activating the first group and deactivatingthe second group to produce light having a first chromaticity, colortemperature, intensity, efficiency, color rendering index, spectralpower distribution, or spatial light distribution, and activating thesecond group and deactivating the first group to produce light having asecond chromaticity, color temperature, intensity, efficiency, colorrendering index, spectral power distribution, or spatial lightdistribution different from the first chromaticity, color temperature,intensity, efficiency, color rendering index, spectral powerdistribution, or spatial light distribution.

The plurality of light-emitting strings may include or consistessentially of a first group of one or more light-emitting strings and,associated with at least one of the light-emitting elements of the firstgroup, a first light-conversion material having a first opticalcharacteristic. The plurality of light-emitting strings may include orconsist essentially of a second group, different from the first group,of one or more light-emitting strings and, associated with at least oneof the light-emitting elements of the second group, a secondlight-conversion material having a second optical characteristicdifferent from the first optical characteristic. The at least onecontrol element may be configured to control the optical characteristicby activating the first group and deactivating the second group toproduce light having a first chromaticity, color temperature, intensity,efficiency, color rendering index, spectral power distribution, orspatial light distribution, and activating the second group anddeactivating the first group to produce light having a secondchromaticity, color temperature, intensity, efficiency, color renderingindex, spectral power distribution, or spatial light distributiondifferent from the first chromaticity, color temperature, intensity,efficiency, color rendering index, spectral power distribution, orspatial light distribution. The plurality of light-emitting strings mayinclude or consist essentially of (i) a first group of one or morelight-emitting strings, and (ii) a second group of one or morelight-emitting strings different from the first group. The at least onecontrol element may be configured to control the optical characteristicby selectively controlling the first and second groups to produce afirst light having a chromaticity, color temperature, intensity,efficiency, color rendering index, spectral power distribution, orspatial light distribution. The at least one control element may beconfigured to control the optical characteristic by selectivelycontrolling the first and second groups to produce a second light havinga chromaticity, color temperature, intensity, efficiency, colorrendering index, spectral power distribution, or spatial lightdistribution, different from the first light. The plurality oflight-emitting strings may include or consist essentially of a firstgroup of one or more light-emitting strings and, associated with atleast one of the light-emitting elements of the first group, a firstoptical element of a first type. The plurality of light-emitting stringsmay include or consist essentially of a second group, different from thefirst group, of one or more light-emitting strings and, associated withat least one of the light-emitting elements of the second group, asecond optical element of a second type different from the first type.The at least one control element may be configured to control theoptical characteristic by selectively controlling the first and secondgroups to produce a first light having a first chromaticity, colortemperature, intensity, efficiency, color rendering index, spectralpower distribution, or spatial light distribution. The at least onecontrol element may be configured to control the optical characteristicby selectively controlling the first and second groups to produce asecond light having a chromaticity, color temperature, intensity,efficiency, color rendering index, spectral light distribution, orspatial light distribution, different from the first light.

The plurality of light-emitting strings may include or consistessentially of a first group of one or more light-emitting strings and,associated with at least one of the light-emitting elements of the firstgroup, a first light-conversion material having a first opticalcharacteristic. The plurality of light-emitting strings may include orconsist essentially of a second group, different from the first group,of one or more light-emitting strings and, associated with at least oneof the light-emitting elements of the second group, a secondlight-conversion material having a second optical characteristicdifferent from the first optical characteristic. The at least onecontrol element may be configured to control the optical characteristicby selectively controlling the first and second groups to produce afirst light having a first chromaticity, color temperature, intensity,efficiency, color rendering index, spectral power distribution, orspatial light distribution. The at least one control element may beconfigured to control the optical characteristic by selectivelycontrolling the first and second groups to produce a second light havinga chromaticity, color temperature, intensity, efficiency, colorrendering index, spectral power distribution, or spatial lightdistribution, different from the first light.

An array of optical elements may each be associated with at least onelight-emitting element, and the array of optical elements may focusand/or shape light from the light-emitting elements to a desiredillumination pattern. At least one optical element may be opticallycoupled to the at least one light-emitting element with no interface toair therebetween. Within one of the light-emitting strings, at least afirst light-emitting element may be associated with an optical elementof a first type, and at least a second light-emitting element may beassociated with an optical element of a second type different from thefirst type. At least one light-emitting element within a firstlight-emitting string may be associated with an optical element of afirst type, and at least one light-emitting element within a secondlight-emitting string, different from the first light-emitting string,may be associated with an optical element of a second type differentfrom the first type. At least one light-emitting element may include orconsist essentially of an LED and a light-conversion material disposedthereon. A conductive layer electrically connected to the first andsecond power conductors may be disposed on a back side of the lightsheetopposite a front side of the lightsheet on which the strings aredisposed. The conductive layer disposed on the back side of a lightsheetmay be electrically connected to the first and second power conductorsby one or more vias (i.e., that extend through a thickness of thelightsheet). An insulating layer may be disposed over at least a portionof the conductive layer disposed on the back side of the lightsheet. Thelightsheet may include at least 200 light-emitting elements. At leastone light-emitting element may include or consist essentially of one ormore semiconductor materials. The one or more semiconductor materialsmay include or consist essentially of silicon, InAs, AlAs, GaAs, InP,AlP, GaP, InSb, GaSb, AlSb, GaN, AlN, InN, and/or mixtures or alloysthereof. The at least one light-emitting element may be aIII-nitride-based LED. At least one light-emitting element may beassociated with a light-conversion material. All or a portion of thelightsheet may be reflective to a range of wavelengths of light emittedby the at least one light-emitting element and/or a range of wavelengthsof light emitted by the light-conversion material. The at least onelight-emitting element may include or consist essentially of alight-emitting diode. The light-conversion material may include orconsist essentially of at least one phosphor. The light-conversionmaterial may include or consist essentially of a binder and a phosphor.The binder may have an index of refraction between about 1.3 and about1.7.

At least a first light-emitting element may be associated with a firstlight-conversion material and (ii) at least a second light-emittingelement, different from the first light-emitting element, may beassociated with a second light-conversion material different from thefirst light-conversion material. Within one of the light-emittingstrings, (i) at least a first light-emitting element may be associatedwith a first light-conversion material and (ii) at least a secondlight-emitting element, different from the first light-emitting element,may be associated with a second light-conversion material different fromthe first light-conversion material. At least one light-emitting elementwithin a first light-emitting string may be associated with a firstlight-conversion material, and at least one light-emitting elementwithin a second light-emitting string, different from the firstlight-emitting string, may be associated with a second light-conversionmaterial different from the first light-conversion material. One of theplurality of light-emitting strings may emit radiation with a firstchromaticity and another one of the plurality of light-emitting stringsmay emit radiation with a second chromaticity different from the firstchromaticity. Within one of the light-emitting strings, one of thelight-emitting elements may emit radiation with a first chromaticity andanother one of the light-emitting elements may emit radiation with asecond chromaticity different from the first chromaticity. Thelightsheet may have a length of at least 0.1 meter, at least 0.5 meters,or at least 3 meters. The lightsheet may include at least 200, or atleast 500, light-emitting elements. The lightsheet may include at least10, or at least 50, light-emitting strings.

The system may include a power connector for connecting a lightsheet toanother lightsheet or to a source of electrical power. The powerconnector may include or consist essentially of at least one crimpconnector. Each light-emitting element may include a substrate that issubstantially transparent to a range of wavelengths of light emitted bythe light-emitting element. The light-emitting elements of at least onefirst light-emitting string may be substantially identical to thelight-emitting elements of at least one second light-emitting stringdifferent from the at least one first light-emitting string. At leastone light-emitting string may emit substantially white light and atleast one light-emitting string emits red light. A carrier may at leastpartially support the lightsheet and include or consist essentially ofglass, polymer, and/or metal.

At least one control element, or even all of the control elements, maybe configured to transmit or receive a control signal. All of thecontrol elements may be configured to transmit or receive the samecontrol signal. At least one of the control elements, or even each ofthe control elements, may be configured to individually transmit orreceive a control signal. At least one control conductor may beconfigured provide a control signal to at least one control element. Atleast one control element may be configured to accept a control signalcomprising at least one of radio waves, microwaves, sound waves,infrared light, visible light and ultraviolet light, or ultrasound. Atleast one control element may be configured to accept a control signalincluding or consisting essentially of an electromagnetic carrier. Atleast one power conductor may be configured to provide a control signalto at least one control element.

In a further aspect, embodiments of the invention feature a lightingsystem that includes or consists essentially of a substantially planarlightsheet, disposed on the lightsheet, first and second spaced-apartpower conductors each extending in a first direction, a plurality oflight-emitting strings, and a plurality of control elements. Eachlight-emitting string (i) includes a plurality of interconnectedlight-emitting diodes (LEDs) spaced along the light-emitting string,(ii) has a first end electrically coupled to the first power conductor,(iii) has a second end electrically coupled to the second powerconductor, and (iv) is oriented in a second direction not parallel tothe first direction. The power conductors supply power to each of thelight-emitting strings and at least one light-emitting string emitswhite light. Each control element (i) is electrically connected to atleast one light-emitting string, (ii) is configured to utilize powersupplied from the power conductors to supply a substantially constantcurrent to the at least one light-emitting string to which it iselectrically connected, and (iii) includes or consists essentially ofone or more resistors and one or more transistors. The lightsheet isseparable, via a cut spanning the first and second power conductors andnot crossing a light-emitting string, into two partial lightsheets eachincluding or consisting essentially of (i) one or more light-emittingstrings, (ii) one or more control elements, and (iii) portions of thefirst and second power conductors configured to supply power to andthereby illuminate the one or more light-emitting strings of the partiallightsheet. For each light-emitting string, a pitch at which the LEDsare spaced is (i) substantially constant and (ii) independent of aposition of the control element electrically connected to thelight-emitting string.

Embodiments of the invention may include one or more of the following inany of a variety of different combinations. At least one of the LEDs maybe a packaged LED. The lightsheet may include a substrate on which theplurality of light-emitting strings is disposed. Each light-emittingstring may include a plurality of conductive elements, disposed over thesubstrate, electrically connecting the plurality of light-emittingelements. An insulating layer may be disposed over at least portions ofsome of the conductive elements. At least one control element mayinclude or consist essentially of an integrated circuit. At least onecontrol element may be configured to control an optical characteristicof the LEDs of the at least one string to which it is electricallyconnected. The optical characteristic may include or consist essentiallyof chromaticity, color temperature, intensity, color rendering index,spectral power distribution, and/or spatial light distribution pattern.At least one light-emitting string may be a folded string having astraight-line length longer than a dimension of the lightsheet spannedby the power conductors. The system may include one or more additionallightsheets each having a tiling direction, and the lightsheet and theone or more additional lightsheets may be connected to each other in thetiling direction at interfaces therebetween. One of the plurality oflight-emitting strings may emit radiation with a first chromaticity andanother one of the plurality of light-emitting strings may emitradiation with a second chromaticity different from the firstchromaticity.

In a further aspect, embodiments of the invention feature a lightingsystem including or consisting essentially of a lightsheet. Thelightsheet includes or consists essentially of a substantially planarflexible substrate, and disposed on the substrate, (i) first and secondspaced-apart power conductors each extending in a first direction and(ii) a plurality of conductive traces. The lighting system includes aplurality of light-emitting strings, each light-emitting string (i)comprising a plurality of interconnected light-emitting elements spacedalong the light-emitting string, (ii) having a first end electricallycoupled to the first power conductor, (iii) having a second endelectrically coupled to the second power conductor, and (iv) beingoriented in a second direction not parallel to the first direction,where the power conductors supply power to each of the light-emittingstrings. The lighting system includes a plurality of control elementseach (i) electrically connected to at least one light-emitting stringand (ii) configured to utilize power supplied from the power conductorsto control the current to the at least one light-emitting string towhich it is electrically connected. The lightsheet has a thickness lessthan 2 mm and has a weight per area of less than 1000 gm/m². Thelightsheet is separable, via a cut (which may be substantiallyperpendicular to the first and second power conductors) spanning thefirst and second power conductors and not crossing a light-emittingstring, into two partial lightsheets each comprising (i) one or morelight-emitting strings, (ii) one or more control elements, and (iii)portions of the first and second power conductors configured to supplypower to and thereby illuminate the one or more light-emitting stringsof the partial lightsheet.

Embodiments of the invention may include one or more of the following inany of a variety of different combinations. The weight per area of thelightsheet may be less than 500 gm/m², less than 200 gm/m², less than100 gm/m², or less than 50 gm/m². The thickness of the lightsheet may beless than 1 mm. The lighting system may include an optical elementdisposed above (and/or connected or fastened to) and spaced apart fromthe lightsheet. The collective thickness of the optical element and thelightsheet may be less than 40 mm, less than 20 mm, or less than 10 mm.The light-emitting elements in each of the light-emitting strings may beseparated by a substantially constant pitch. The light-emitting elementsmay be separated by a substantially constant pitch between differentstrings, and this pitch may be substantially equal to the pitchseparating light-emitting elements within the light-emitting strings. Atleast one light-emitting element may emit substantially white light. Atleast one light-emitting element may include or consist essentially of abare-die light-emitting diode. At least one light-emitting element mayinclude or consist essentially of a packaged light-emitting diode. Apower supply configured to provide a substantially constant voltage tothe power conductors may be electrically connected to the powerconductors.

In at least one light-emitting string, at least one (or even each)light-emitting element is coupled to conductive traces on the substratevia a solder. The solder may include or consist essentially of bismuthand/or indium. The solder may have a liquidus temperature less than 165°C., less than 150° C., or less than 130° C. The solder may include orconsist essentially of 50% to 65% bismuth and 35% to 50% tin. The soldermay include 0.25% to 3% silver. The solder may include or consistessentially of 20% to 40% bismuth, 40% to 60% indium, and 8% to 25% tin.The lightsheet may be flexible. A conductive joint may electricallycouple two discrete regions of the lightsheet at a joint region. Theflexibility of the lightsheet at the joint region (and proximate theconductive joint) may be approximately equal to the flexibility of thelightsheet at a region spaced away from the joint region. The conductivejoint may include or consist essentially of solder. The conductive jointmay electrically couple (a) portions of the first power conductor oneach region of the lightsheet or (b) portions of the second powerconductor on each region of the lightsheet. The conductive joint may beflexible. The conductive joint may include at least one undulationtherewithin. The conductive traces may include or consist essentially ofcopper, brass, aluminum, silver, and/or gold. The thickness of theconductive traces may be less than 50 μm and the lightsheet may includeor consist essentially of polyethylene terephthalate. The thickness ofthe lightsheet may be less than 100 μm.

In another aspect, embodiments of the invention feature a lightingsystem including or consisting essentially of a lightsheet. Thelightsheet includes or consists essentially of a substantially planarflexible substrate (i) including or consisting essentially ofpolyethylene terephthalate and (ii) having a thickness less than 100 μm.Disposed on the substrate are first and second spaced-apart powerconductors each (i) extending in a first direction, (ii) including orconsisting essentially of aluminum and/or copper, and (iii) having athickness less than 50 μm. Disposed on the substrate are a plurality ofconductive traces each (i) including or consisting essentially ofaluminum and/or copper, and (ii) having a thickness less than 50 μm. Thelighting system includes a plurality of light-emitting strings, eachlight-emitting string (i) comprising, spaced along the light-emittingstring, a plurality of interconnected light-emitting diodes eachemitting substantially white light, (ii) having a first end electricallycoupled to the first power conductor, (iii) having a second endelectrically coupled to the second power conductor, and (iv) beingoriented in a second direction not parallel (e.g., perpendicular) to thefirst direction, where the power conductors supply power to each of thelight-emitting strings. The lighting system includes a plurality ofcontrol elements each (i) electrically connected to at least onelight-emitting string and (ii) configured to utilize power supplied fromthe power conductors to control the current to the at least onelight-emitting string to which it is electrically connected. Thelightsheet has a thickness less than 1.5 mm and has a weight per area ofless than 400 gm/m². The lightsheet is separable, via a cut (which maybe substantially perpendicular to the first and second power conductors)spanning the first and second power conductors and not crossing alight-emitting string, into two partial lightsheets each comprising (i)one or more light-emitting strings, (ii) one or more control elements,and (iii) portions of the first and second power conductors configuredto supply power to and thereby illuminate the one or more light-emittingstrings of the partial lightsheet.

These and other objects, along with advantages and features of theinvention, will become more apparent through reference to the followingdescription, the accompanying drawings, and the claims. Furthermore, itis to be understood that the features of the various embodimentsdescribed herein are not mutually exclusive and can exist in variouscombinations and permutations. Reference throughout this specificationto “one example,” “an example,” “one embodiment,” or “an embodiment”means that a particular feature, structure, or characteristic describedin connection with the example is included in at least one example ofthe present technology. Thus, the occurrences of the phrases “in oneexample,” “in an example,” “one embodiment,” or “an embodiment” invarious places throughout this specification are not necessarily allreferring to the same example. Furthermore, the particular features,structures, routines, steps, or characteristics may be combined in anysuitable manner in one or more examples of the technology. As usedherein, the terms “about,” “approximately,” and “substantially”mean±10%, and in some embodiments, ±5%. The term “consists essentiallyof” means excluding other materials that contribute to function, unlessotherwise defined herein. Nonetheless, such other materials may bepresent, collectively or individually, in trace amounts.

Herein, two components such as light-emitting elements and/or opticalelements being “aligned” or “associated” with each other may refer tosuch components being mechanically and/or optically aligned. By“mechanically aligned” is meant coaxial or situated along a parallelaxis. By “optically aligned” is meant that at least some light (or otherelectromagnetic signal) emitted by or passing through one componentpasses through and/or is emitted by the other.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference characters generally refer to the sameparts throughout the different views. Also, the drawings are notnecessarily to scale, emphasis instead generally being placed uponillustrating the principles of the invention. In the followingdescription, various embodiments of the present invention are describedwith reference to the following drawings, in which:

FIGS. 1A and 1B are schematic plan views of lighting systems inaccordance with various embodiments of the invention;

FIGS. 2A-2C are schematic illustrations of electrical configurations oflighting systems in accordance with various embodiments of theinvention;

FIGS. 3 and 4 are schematic plan views of lighting systems in accordancewith various embodiments of the invention;

FIGS. 5A-5I, 6A, and 6B are schematic illustrations of electricalconfigurations of lighting systems in accordance with variousembodiments of the invention;

FIG. 7 is a flow chart depicting a process flow for manufacture oflighting systems in accordance with various embodiments of theinvention;

FIG. 8A is a schematic cross-section of a lighting system in accordancewith various embodiments of the invention;

FIG. 8B is a schematic plan view of a lighting system in accordance withvarious embodiments of the invention;

FIGS. 9A and 9B are a schematic cross-section and plan view,respectively, of a lighting system in accordance with variousembodiments of the invention;

FIGS. 10A-10E are schematic illustrations of vias in a lighting systemin accordance with various embodiments of the invention;

FIG. 11 is a schematic illustration of a lighting system in accordancewith various embodiments of the invention;

FIGS. 12 and 13 are schematic illustrations of electrical configurationsof lighting systems in accordance with various embodiments of theinvention;

FIG. 14 is a schematic cross-section of a lighting system in accordancewith various embodiments of the invention;

FIGS. 15, 16, and 17 are schematic illustrations of lighting systems inaccordance with various embodiments of the invention;

FIG. 18 is a schematic cross-section of a lighting system in accordancewith various embodiments of the invention;

FIG. 19 is a schematic illustration of a connector for a lighting systemin accordance with various embodiments of the invention;

FIGS. 20, 21A, 21B, and 22A are schematic illustrations of a lightingsystem in accordance with various embodiments of the invention;

FIG. 22B is a schematic circuit diagram of a lighting system inaccordance with various embodiments of the invention;

FIG. 23 is a schematic illustration of a lighting system in accordancewith various embodiments of the invention;

FIG. 24 is a schematic illustration of a lighting system in accordancewith various embodiments of the invention;

FIGS. 25A and 25B are schematic illustrations of an element of alighting system in accordance with various embodiments of the invention;

FIG. 26 is a schematic cross-section of a light-emitting element inaccordance with various embodiments of the invention;

FIGS. 27 and 28 are schematic cross-sections of light-emitting elementsintegrated with phosphor materials in accordance with variousembodiments of the invention;

FIG. 29 is a schematic illustration of a light-emitting element bondedto a substrate in accordance with various embodiments of the invention;

FIGS. 30A, 30B, and 30C are schematic illustrations of electricalconfigurations of light-emitting elements and control elements inaccordance with various embodiments of the invention;

FIGS. 31, 32A-32D, and 33 are schematic illustrations of lightingsystems featuring control elements in accordance with variousembodiments of the invention;

FIGS. 34A-34K are schematic cross-sections of portions of lightsheets atleast partially connected by joining elements in accordance with variousembodiments of the invention;

FIG. 34L is a schematic plan view of portions of lightsheets at leastpartially connected by joining elements in accordance with variousembodiments of the invention;

FIG. 35 is a schematic illustration of a lightsheet in accordance withvarious embodiments of the invention; and

FIG. 36 is a schematic illustration of a lighting system in accordancewith various embodiments of the invention.

DETAILED DESCRIPTION

FIGS. 1A-1B are schematic drawings of an electronic device (or“lightsheet”) 100 in accordance with embodiments of the presentinvention. For convenience purposes, the “width” of electronic device100 refers to the short side of the rectangle while the “length” refersto the long side of the rectangle. While electronic device 100 is shownas a rectangle, this is not a limitation of the present invention, andin other embodiments electronic device 100 may be square, circular, orhave any other shape. In various embodiments, the shape of electronicdevice 100 is engineered such that it may be tiled in one or moredirections (as detailed below). In some embodiments, the lightsheet mayhave a width in the range of about 1 inch to about 24 inches and alength in the range of about 1 inch to about 50 feet; however, this isnot a limitation of the present invention, and in other embodiments thelength and/or width of the lightsheet may have any values.

Referring to FIG. 1B, lightsheet 100 features an array of light-emittingelements (LEEs) 130 each electrically coupled between conductive traces160, and power conductors 110 and 120 providing power to conductivetraces 160 and control elements (CEs) 140, all of which are disposedover a substrate 165. As utilized herein, a “wiring board” refers to asubstrate for LEEs with or without additional elements such asconductive traces or CEs. A wiring board may also be referred to as asubstrate or a circuit board. FIG. 1B shows an enlarged portion oflightsheet 100. In the exemplary embodiment depicted in FIG. 1B, powerconductors 110, 120 are spaced apart from each other and light-emittingstrings (or simply “strings”) 150 are connected in parallel across powerconductors 110, 120. In some embodiments, for example as shown in FIG.1B, strings 150 do not cross (i.e., intersect) each other. In otherwords, power conductors 110, 120 are oriented in one direction andstrings 150 are oriented such that they span power conductors 110, 120in a different direction. As shown in FIG. 1B, strings 150 aresubstantially perpendicular to power conductors 110, 120. However, thisis not a limitation of the present invention, and in other embodiments,for example as shown in FIGS. 5C-5E, at least some segments (i.e.,portions connecting two or more LEEs 130), or even the entire strings150, generally define a line that is not perpendicular to powerconductors 110, 120 yet is (at least for an entire string 150) notparallel to power conductors 110, 120. Notably, in the examples shown inFIGS. 5C-5E, strings 150 are still non-intersecting and do not crosseach other. However, this is not a limitation of the present invention,and in other embodiments strings 150 may intersect, for example onestring 150 splitting into two or more strings 150, or two or morestrings 150 joining to form a reduced number of strings 150, as shown inin FIGS. 5F-5G. FIGS. 5F-5G show strings 150 splitting at the joint withpower conductor 120; however, this is not a limitation of the presentinvention, and in other embodiments strings 150 may split at the jointwith power conductor 110, or strings 150 may split anywhere between LEEs130 and/or CE 140. In some embodiments, as described herein, for examplein reference to FIGS. 25A and 25B, conductive elements may cross overeach other without being electrically coupled, and in some embodimentsstrings 150 may cross over or under each other, as shown in FIG. 5H.While the examples discussed with respect to FIGS. 5A-5H show LEEs 130and strings 150 between power conductors 110, 120 this is not alimitation of the present invention and in other embodiments all or aportion of one or more strings 150 may be outside of power conductors110, 120. For example FIG. 5I shows a portion of string 150 extendingbeyond power conductors 110, 120.

As shown, LEEs 130 are positioned across substrate 165 in a regularperiodic array, although this is not a limitation of the presentinvention and in other embodiments LEEs 130 may occupy any positions onlightsheet 100. Power conductors 110 and 120 provide power to each LEEstring, for example the string 150 encircled by the dashed line in FIG.1B. Each LEE string 150 typically includes multiple conductive traces160 that interconnect multiple LEEs 130, as well as one or more CEs 140,which in FIG. 1B is in series with LEEs 130. String 150 shown in FIG. 1Bis a folded string, i.e., a string that has three segments electricallycoupled in series but positioned as three adjacent segments. A stringsegment is a portion of a string spanning all or a portion of the regionbetween power conductors 110 and 120 in FIG. 1B. In lightsheet 100, somestring segments include LEEs 130 while others do not. However, in otherembodiments the distribution and position of LEEs 130 along conductiveelements 160 and string segments may be different. In some embodiments,a string 150 may be a straight string, that is a string with no folds(as shown schematically in FIG. 3). One end of string 150 iselectrically coupled to power conductor 110, while the other end ofstring 150 is electrically coupled to power conductor 120. As will bediscussed, the number of segments in a string 150 is not a limitation ofthe present invention.

FIGS. 1A and 1B illustrate three aspects in accordance with embodimentsof the present invention. The first is the multiple strings 150 that arepowered by the set of power conductors 110, 120. The second is thepositional relationship between the locations of LEEs 130 and CE 140,which is disposed between the conductive traces 160 and between powerconductors 110,120. The third is the inclusion of a CE 140 in eachstring of series-connected LEEs 130. Combinations of these three aspectsenable electronic device 100 to be economically manufactured in verylong lengths, for example in a roll-to-roll process, and cut tospecified lengths, forming lightsheets, while maintaining the ability totile, or place lightsheets adjacent to each other (e.g., in the lengthdirection), with no or substantially no change in pitch between LEEs 130or in the optical characteristics across the joint between two adjacentlightsheets, as discussed in more detail below.

In an exemplary embodiment, CE 140 is configured to maintain a constantor substantially constant current through LEEs 130 of string 150. Forexample, in some embodiments, the constant voltage applied to powerconductors 110, 120 may vary, or the sum of the forward voltages of LEEs130 in different strings may be somewhat different, for example as aresult of manufacturing tolerances, or the component and/or operationalvalues of the element(s) within CE 140 may vary, for example as a resultof manufacturing tolerances or changes in operating temperature, and CE140 acts to maintain the current through LEEs 130 substantially constantin the face of these variations. In other words, the input to thelightsheet is a constant voltage that is applied to power conductors110, 120, and CEs 140 convert the constant voltage to a constant orsubstantially constant current through LEEs 130. As will be describedherein, the design of CE 140 may be varied to provide different levelsof control or variation of the current through LEEs 130. In someembodiments, CEs 140 may control the current through LEEs 130 to besubstantially constant with a variation of less than about ±25%. In someembodiments, CEs 140 may control the current through LEEs 130 to besubstantially constant with a variation of less than about ±15%. In someembodiments, CEs 140 may control the current through LEEs 130 to besubstantially constant with a variation of less than about ±10%. In someembodiments, CEs 140 may control the current through LEEs 130 to besubstantially constant with a variation of less than about ±5%.

In some embodiments, as detailed herein, CEs 140 may, in response to acontrol signal, act to maintain a constant or substantially constantcurrent through LEEs 130 until instructed to change to a differentconstant or substantially constant current, for example by an externalcontrol signal. In some embodiments, as detailed herein, all CEs 140 ona sheet may act in concert, that is maintain or change the currentthrough all associated LEEs 130; however, this is not a limitation ofthe present invention, and in other embodiments one or more CEs 140 maybe individually instructed and/or energized.

FIG. 2A depicts an exemplary circuit topography in accordance withembodiments of the present invention that features conductive traces160, at least two power conductors 110, 120, multiple LEEs 130, and CE140. In some embodiments, LEEs 130 may be configured in a regularperiodic array having a pitch (i.e., distance between adjacent LEEs 130)220, as shown in FIG. 2A. FIG. 2A shows two power conductors 110 and120, which may be used to provide power to strings of LEEs 130, as wellas a string 150. Each string 150 may include two or more electricallycoupled LEEs 130. LEEs 130 in string 150 may be electrically coupled inseries, as shown in FIG. 2A; however, this is not a limitation of thepresent invention and in other embodiments other examples of electricalcoupling may be utilized, for example LEEs in parallel or in anycombination of series and parallel connections. FIG. 2A shows CE 140 inseries with string 150; however, this is not a limitation of the presentinvention and in other embodiments CE 140 may have different electricalcoupling between power conductors 110, 120. For example, FIG. 2B showsCE 140 separately electrically coupled to power conductors 110, 120 andthe LED string, while FIG. 2C shows each CE 140 electrically coupled totwo strings. The number of strings electrically coupled to each CE 140is not a limitation of the present invention. Combinations of structuresshown in FIGS. 2A-2C, as well as other electrical connections, all fallwithin the scope of the present invention. Power conductors 110, 120 maybe used to provide power to strings 150, for example AC power, DC power,or power modulated by any other means.

Lightsheets may be produced as individual components or in aroll-to-roll format. Lightsheets of different lengths, where forconvenience the length is identified by the double-headed arrow 305 inFIG. 3, may be separated from a roll and sold as separate products.Herein, a lightsheet may refer to a cut or segmented portion of a largerlength, for example the structures shown in FIGS. 1A and 1B, and beforecutting or separation, the larger length may also be referred to as alightsheet or “lightsheet web.” Thus, one lightsheet web of constantwidth, i.e., the direction perpendicular to direction 305, may be usedfor a wide variety of lightsheet products of different lengths. Forexample, FIG. 3 shows a lightsheet 360 or lightsheet web that may have awidth of about 10 cm and a pitch (identified as dimension 220 in FIG.2A) between LEEs 130 of about 1 cm. The square identified as 310 in FIG.3 has sides equal in length to pitch 220. Thus, in this example thelength of a particular lightsheet may be selected in any increment ofabout 1 cm by separating the lightsheet web 360 between two adjacentstrings 150. For example lightsheet 360 shown in FIG. 3 may be segmentedinto a lightsheet that is four strings long and a lightsheet that is sixstrings long by cutting or separating along cut line 320.

In embodiments where the lightsheet includes or consists essentially offolded strings, the distance between adjacent strings (i.e., the “stringpitch”) may be different from the LEE pitch (i.e., the distance betweenadjacent LEEs on a string). For reference, in FIG. 3B the string pitchis substantially the same as the LEE pitch. FIG. 1B shows an example ofan embodiment having a folded string in which the string pitch is largerthan the LEE pitch. In some embodiments, the string pitch may be equalto or substantially equal to the spacing between CEs 140, as shown inFIG. 1B; however, this is not a limitation of the present invention. Insome embodiments, the string pitch is an integer multiple orsubstantially an integer multiple of the LEE pitch. For example, in someembodiments the LEE pitch is the same across all strings, includingembodiments including or consisting essentially of folded strings, andin some of these embodiments the string pitch is an integer multiple orsubstantially an integer multiple of the LEE pitch. For example, in FIG.1B the string pitch is about four times the LEE pitch. In reference toFIG. 5A, the string pitch is about three times the LEE pitch, in FIG.5C, the string pitch is about twice the LEE pitch, and in FIG. 6B, thestring pitch is about five times the LEE pitch. However, this is not alimitation of the present invention, and in other embodiments the stringpitch may not be an integer multiple or substantially an integermultiple of the LEE pitch.

Cutting or segmenting lightsheet web 360 into smaller lightsheets may becarried out by a wide variety of techniques, for example knife cutting,laser cutting, or the like. The method of segmentation is not alimitation of the present invention. In one embodiment, segmentationoccurs at the midpoint or substantially at the midpoint between adjacentstrings, as discussed in more detail below.

Lightsheet segmentation may occur at any point in the manufacturingprocess, for example after formation of the substrate 165, afterformation of LEEs 130 and/or CEs 140 over substrate 165 (FIG. 1B), or asthe final step of the manufacturing process. Segmentation may occurbefore or after optional testing. Furthermore, completed or partiallycompleted lightsheets or lightsheet webs may be inventoried or storedfor a period of time, after which manufacture may be completed, ifnecessary, and/or the lightsheet or lightsheet web segmented.Segmentation may be performed on a just-in-time basis or on anorder-by-order basis. In some embodiments, lightsheets or lightsheetwebs may be segmented in the field. In some embodiments, segmentation isperformed by cutting with a scissors or knife. In some embodiments,segmentation may occur after installation, for example to change thesize of the lightsheet or to remove and replace a damaged ornonfunctional lightsheet or portion of a lightsheet, or to fit in aluminaire or architectural feature of a specific dimension.

In addition, individual lightsheets 360 may be tiled with little or nosubstantial change in pitch or variation in optical characteristicsacross the joint. In some embodiments tiling may be enabled in onedirection, i.e., length or width, for example the length identified byarrow 305 in FIG. 3, while in other embodiments tiling may be enabled inmore than one direction.

In one embodiment, tiling is achieved by segmenting one or morelightsheets or lightsheet webs between adjacent strings 150. In someembodiments, lightsheets or lightsheet webs are segmented at themidpoint or substantially at the midpoint between adjacent strings 150,such that the distance between the last string and the edge of sheet 360is one-half of the string pitch, as shown in FIG. 4, and thenpositioning the lightsheets adjacent to each other at their “tilingedges.” FIG. 4 shows two wiring boards 360, 360′ that are tiled togethersuch that there is no difference, or no substantial difference, inspacing between the strings on adjacent sides of a joint 410therebetween. Because there is no or almost no difference in spacingbetween the strings on adjacent sides of the joint 410, the opticalcharacteristics appear uniform across the joint 410, i.e., thelightsheet appears to be “joint-free.” In some embodiments of thepresent invention such joint-free tiling may occur in the orthogonaldirection, i.e., perpendicular to the direction 305 (FIG. 3), forexample if power conductors 110, 120 occupy less than one-half of thepitch distance, or by other means, which will be discussed later. Insome embodiments, segmentation may be accomplished by removing one ormore portions of strings or adjacent strings 150. In some embodimentssuch joint-free tiling may occur in non-orthogonal directions, forexample for non-square or non-rectangular lightsheets.

In some embodiments of the present invention, the pitch is determined atleast in part by the desired wiring board width, the string voltage, theLEE voltage at the desired operating current (e.g., the forward voltageof an LED), and the LEE pitch (i.e., the spacing between individualLEEs). The string voltage may be determined by various constraints, forexample the desired or available power for powering the system,certification issues or the like. In one embodiment, the design processstarts with the forward voltage of the LEE V_(f), the specified stringvoltage V_(s), and LEE pitch p. The number of LEEs in a string is givenapproximately by n=V_(s)/V_(f). The physical string length is then givenapproximately by the product of the pitch and the number of LEEs, i.e.,(n−1)×p. In some embodiments of this approach, n may not be an integerand adjustments to n or p may be employed to make n an integer. Inanother embodiment, adjustments to V_(f), for example by changing theoperating current or temperature, or to V_(s), by changing the designrequirement, may also be employed, for example to make n an integer.

In some embodiments, the physical string length, i.e., the length of thestring if it were laid out in a straight line, is larger than thedesired wiring board width and in this case the string may be folded ortwisted to fit within the desired wiring board width, for example asshown in FIGS. 5A-5C, in which LEEs 130 are shown schematically ascircles for clarity. FIGS. 5A-5C depict several examples of “folding” astring. FIGS. 5A and 5B show one string, while FIG. 5C shows threestrings, all with approximately the same pitch. In one embodiment, LEEs130 are positioned in a regular periodic array, with a fixed pitchbetween LEEs 130, and the power conductors that electricallyinterconnect them as a string may have any layout that fits within theconstraints of the LEE pitch. In other embodiments, LEEs 130 may bepositioned in other ways; the position of LEEs 130 and the configurationof the power conductors that interconnect LEEs 130 within one string arenot limitations of the present invention. In various embodiments thedesign process may start with different constraints, for exampleincluding one or more of these characteristics: lumen or optical powerdensity per unit area, lumen or optical power per LEE 130, pitch, cost,luminous efficacy, electrical power per unit area, electrical power perLEE 130, or the like.

While FIGS. 5A-5C show folding of strings into a plurality of parallelsegments, this is not a limitation of the present invention and in otherembodiments, the string segments may not all be parallel, or may formdifferent angles relative to each other or the edges of substrate 165(FIG. 1B), for example as shown in FIGS. 5D and 5E. The orientation ofthe strings and/or portions or segments of the strings is not alimitation of the present invention. In some embodiments, multiple LEEs130 in one or more strings 150 may be oriented to form various shapes,pictures, images, letters, or the like. Such embodiments may be used fordecorative purposes, signage, or other applications. As discussedherein, FIGS. 5F and 5G show examples of split strings, while FIG. 5Hshows an example of crossed-over strings and FIG. 5I shows an example ofa string extending beyond (i.e., outside of) power conductors 110, 120.

Another aspect of embodiments of the present invention may be realizedin reference to FIGS. 5A and 5B. While LEEs 130 are shown as circles inthese figures, in some embodiments LEEs 130 may have a polarity, forexample p- and n-sides in the case of an LEE 130 being an LED or laser.In such embodiments, the conductive traces may be configured such thatall LEEs 130 are oriented in one direction, for example with thepositive or cathode end of each LEE 130 oriented or pointed in the samedirection. FIG. 5B shows one embodiment of such a configuration ofconductive trace 160; however, this configuration is not a limitation ofthe present invention and in other embodiments other configurations ofconductive traces 160 may be employed to achieve polarity orientation ofLEEs 130. In some embodiments, LEEs 130 may not all have the samepolarity orientation. The polarity orientation of the plurality of LEEs130 is not a limitation of the present invention.

In a first exemplary embodiment, V_(s)=60 V, V_(f)=3.0 V and p=1 cm.This results in 20 LEDs per string and a “straight” string length ofabout 19 cm between the first and last LEDs. FIG. 6A shows an examplewhere the string is straight, resulting in a sheet that has a widthequal to the string length (19 cm) plus additional space on each edgefor the power conductors. The lightsheet in FIG. 6A has a length of m×p,where m is the number of strings on the sheet. If the number of stringson the sheet m is 20, then the total length of the sheet is about 20 cm.

In the first exemplary embodiment above, V_(s)=60 V, V_(f)=3.0 V and p=1cm. This results in 20 LEDs per string and a “straight” string length ofabout 19 cm between the first and last LED. FIG. 6B shows an examplewhere the sheet is relatively narrower than the straight string length,for example in the range of about 1 cm to about 5 cm. In this case thenumber of LEDs 130 between power conductors 110 and 120 is 4 (in astraight line) and the string forms a 4×5 array, as shown in FIG. 6B,with each string segment having a length of about 3 cm. The wiring boardin FIG. 6B has a length of m_(s)×p, where m_(s) is the number of stringsegments on the sheet. In this example there are 10 string segments,resulting in a total length of about 10 cm. In this example the stringpitch is about five times the LEE pitch. Similarly, the total length ofabout 10 cm may be determined from the product of the number of strings(two) and the string pitch (five).

As detailed herein, the wiring boards shown in FIGS. 6A and 6B may betiled together in the length direction such that the distance betweenadjacent LEEs across a joint is the same as the LEE pitch p, resultingin uniform lighting characteristics with virtually no change at or nearthe joint region.

The examples shown in FIGS. 6A and 6B provide an example of furtherembodiments of the present invention. In some embodiments, it may bedesirable to manufacture lightsheets of different width, but able tooperate on the same voltage. In these embodiments, the string voltage ispreferably the same or substantially the same for each different-widthlightsheet. In one embodiment, this may be accomplished by using stringswith the same number of LEEs 130 per string and folding the strings tofit the different widths. In order to be able to produce a relativelylarger number of different width lightsheets, the number of LEEs 130 ina string may be advantageously determined to be a value with arelatively large number of divisors (or “factors”). Table 1 shows anexample of different configurations for strings including or consistingessentially of 4 to 25 LEEs 130. In Table 1, the entry A×B means “A”string segments and “B” LEEs per string segment. For example, 1×16 meansa straight string with 16 LEEs per string and 3×4 means a string with 12LEEs, configured in 3 string segments, each having 4 LEEs per stringsegment. As may be seen from Table 1, strings having any prime number ofLEEs 130 generally cannot be folded. Strings including or consistingessentially of 12, 18, or 20 LEEs 130 may have 5 folded configurations(Table 1 does not include the case of a string containing only a singleLEE 130). Strings including or consisting essentially of 24 LEEs 130 mayhave 7 folded configurations.

The number of configurations may be determined by taking the quantity offactors of for a particular number and subtracting one, to eliminate thesingle-LEE string. Table 2 shows the number of folded stringconfigurations for strings including or consisting of LEEs from 30 to220. Table 2 may be used to determine the number of different foldedstring configurations for different numbers of LEEs per string.

In some embodiments, it may be desirable to limit the voltage suppliedto the lightsheet and/or to limit the power supplied to one or moreelectrically coupled lightsheets. For example, in the United States, aclass 2 UL electrical certification requires that the voltage not exceed60V and the power not exceed 100 watts. For such class 2 configurations,strings including or consisting essentially of 12, 16, 18, or 20 LEEs130 may be advantageously chosen to permit a relatively large number oflightsheet width configurations.

For higher voltage strings, Table 2 may be used to advantageously selectthe number of LEEs per string to achieve any number of folded stringconfigurations. As may be seen from Table 2, strings including orconsisting essentially of 60, 72, 84, 90, 96, 108, 126, 140, 150, 156,160, 198, 200, 204, and 211 LEEs have 11 folded string configurations.As may be seen from Table 2, strings including or consisting essentiallyof 144 LEEs have 14 folded string configurations. As may be seen fromTable 2, strings including or consisting essentially of 120, 168, 210,and 216 LEEs have 15 folded string configurations. As may be seen fromTable 2, strings including or consisting essentially of 180 LEEs have 17folded string configurations.

TABLE 1 LEEs Per String Folded String Configurations 4 1 × 4  2 × 2 5 1× 5  6 1 × 6  2 × 3 3 × 2 7 1 × 7  8 1 × 8  2 × 4 4 × 2 9 1 × 9  3 × 310 1 × 10 2 × 5 5 × 2 11 1 × 11 12 1 × 12 2 × 6 3 × 4 4 × 3 6 × 2 13 1 ×13 14 1 × 14 2 × 7 7 × 2 15 1 × 15 3 × 5 5 × 3 16 1 × 16 2 × 8 4 × 4 8 ×2 17 1 × 17 18 1 × 18 2 × 9 3 × 6 6 × 3 9 × 2 19 1 × 19 20 1 × 20  2 ×10 4 × 5 5 × 4 10 × 2  21 1 × 21 3 × 7 7 × 3 22 1 × 22  2 × 11 11 × 2 23 1 × 23 24 1 × 24  2 × 12 3 × 8 4 × 6 6 × 4 8 × 3 12 × 2 25 1 × 25 5 ×5

TABLE 2 Number of Folded String LEEs Per String Configurations 30 7 36 840 7 42 7 48 9 54 7 60 11 66 7 70 7 72 11 80 9 84 11 90 11 96 11 100 8102 7 104 7 108 11 112 9 120 15 126 11 135 7 136 7 138 7 140 11 144 14150 11 152 7 156 11 160 11 162 9 165 7 168 15 170 7 174 7 176 9 180 17182 7 184 7 186 7 189 7 190 7 192 13 195 7 196 8 198 11 200 11 204 11208 9 210 15 216 15 220 11

FIG. 7 is a flow chart of a design process that may be used in oneembodiment of this invention. The number of steps shown in the processshown in FIG. 7 is not a limitation of the present invention, and inother embodiments such processes have more or fewer steps and/or thesteps may be performed in different orders. In step 710 the forwardvoltage of the LEE at the operating current and conditions isdetermined. In step 715 the total string voltage is determined. In step720 the number of LEEs in each string is determined by dividing thetotal string voltage by the LED forward voltage. In step 725 the desiredpitch is determined. In step 730 the “straight-line” string length isdetermined by multiplying the number of LEDs per string by the pitch. Instep 735 the desired wiring board width is determined. In step 740 thestraight-line string length is compared to the desired wiring boardwidth. If the desired wiring board width is approximately the same asthe straight-line string length, then a straight string may be used, inwhich case each string is separated from the adjacent string by the LEDpitch, as shown in steps 745 and 750. If the desired wiring board widthis less than the straight line string length, then a folded string isused, as shown in steps 760 and 765. The number of string segments maythen be calculated initially by dividing the straight string length bythe desired wiring board width, as shown in step 770. Some adjustment oriteration steps may be required to adjust the parameters to achieve thedesired layout, as shown in step 775. This adjustment may take the formof using a different interconnect topology, for example like those shownin FIGS. 5A-5C, or may take the form of adjusting the pitch, V_(f) ofthe LEDs, number of LEEs per string, string voltage, or the like. Insome embodiments, the order of steps shown in FIG. 7 may be changed, orsome steps omitted or other steps added or repeated. In someembodiments, the order is modified when different initial constraintsare utilized. For example, in FIG. 7 the initial constraints include theLEE forward voltage and the string voltage; in another embodiment theinitial constraints may include, for example, the number of LEEs in eachstring, or the desired light output power of each LEE, the desired lightpower density, the desired electrical power density, the cost, or thelike, which may determine the operating conditions, leading to aparticular forward voltage.

If the desired width of the wiring board or lightsheet is larger thanthe straight-line string voltage, several approaches may be used. In oneembodiment, wiring boards with a smaller width may be tiled together inthe width direction; however, with the structures discussed above, theLEEs on adjacent sides of the joint in the width direction may not havethe same pitch as the LEEs on the wiring board due to the presence ofpower conductors 110 and 120. Another approach is to modify some of theparameters to achieve a longer straight-line string length, per the flowchart in FIG. 7, for example by increasing the string voltage orincreasing the LEE pitch.

In step 715 the total string voltage is determined. In some embodimentsa string may include one or more CEs 140, which may have their ownvoltage requirements (i.e., to account for a voltage drop across CEs140). If present, this voltage drop may be taken into account whendetermining the total string voltage, which also includes the voltageacross the LEEs 130 in each string. In some embodiments it may also benecessary to include the voltage drop across the conductive elements(traces) in each string and/or in the power conductors.

In some embodiments, power conductors 110 and 120 provide a fixed orsubstantially fixed voltage to each string, and that voltage may belarger than the string voltage discussed above, for example toaccommodate voltage taken up by CEs 140. For example, if the stringvoltage discussed above is the voltage across only the LEEs in eachstring; then the voltage across power conductors 110 and 120, forexample in FIGS. 6A and 6B, may be V_(f)×n+V_(CE), where V_(CE) is thevoltage across CEs 140. In some embodiments, the voltage supplied acrosspower conductors 110 and 120 and thus the supplied string voltage mayvary, for example because of variations in the input power source,changes in temperature, variations in component characteristics (forexample LED I-V characteristics or the characteristics of CEs 140) orthe like. Such variations may be accommodated and techniques for doingso are described herein.

In some embodiments, it may be desirable to increase the conductivity ofpower conductors 110, 120 and or conductive elements 160. For example,power conductors 110, 120 formed on substrate 165 may have anundesirably large resistance, resulting in an undesirably large voltagedrop across power conductors 110, 120 in operation causing a reductionin efficiency or luminous efficacy or even the inability to turn on oneor more strings, if the voltage is reduced sufficiently. In someembodiments, this may be accommodated by modifying the voltage requiredto power each string. In some embodiments, the voltage level on powerconductors 110, 120 may change along the lengths of the powerconductors. For example, the voltage level may decrease in a directionaway from the point of connection to the power source because, e.g., ofthe resistance in the power conductors. In some embodiments, the voltageto energize each string may then be designed to follow the availablevoltage along the power conductor, for example by changing the voltagedrop across CE 140, conductive elements 160 and/or reducing the numberof LEEs 130 in the string.

In some embodiments, power conductors 110, 120 may be formed using ahigher conductivity material than that used for conductive traces 160.In some embodiments, power conductors 110, 120 may be formed of the samematerial as that used for conductive traces 160, but may have arelatively larger thickness or relatively larger width orcross-sectional area than that used for conductive traces 160, thusdecreasing their resistance. In some embodiments, power conductors 110,120 may have multiple layers of the same or different materials.

In some embodiments, an additional conductive path may be formed inparallel with all or parts of power conductors 110, 120 in order toreduce the total resistance. This may be advantageous in embodimentswhere multiple lightsheets 360 are connected together and powered by asingle power supply or where lightsheet 360 is relatively long, forexample at least about 1 meter, or at least 5 meters, or at least 10meters long. In some embodiments the conductivity of power conductors110, 120 and/or conductive elements 160 may not be sufficiently high toachieve a desired value of voltage drop in the conductors. Such asituation may lead to undesirably high resistance losses, leading to aloss in luminous efficacy of the lighting system and/or undesirableheating of the conductors. In some embodiments, a conductive materialmay be formed over and in electrical contact with all or portions ofpower conductors 110, 120. For example, a conductive tape 810,optionally including a conductive adhesive, may be formed over oradhered to power conductors 110, 120 to decrease their resistance, asshown in FIG. 8A. An example of such a conductive tape is 3M 1183 tape.In some embodiments, a separate conductive path 820, which may includeor consist essentially of a wire or other conductive material, may beelectrically coupled in parallel to portions of power conductors 110,120, as shown in FIG. 8B, which depicts wire 820 with optionalinsulation 830. Wire 820 may be electrically attached to powerconductors 110,120 by various techniques, for example solder ormechanical crimp connectors. In some embodiments, the separateconductive path 820 may include or consist essentially of all or aportion of the frame, fixture, or enclosure into which the lightsheet isplaced. In some embodiments, the separate conductive path 820 mayinclude or consist essentially of all or a portion of the hardware ormounting equipment with which the lightsheet is mounted.

Various embodiments of the invention may include a carrier for one ormore lightsheets. For example, as discussed above, the lightsheet may beinstalled in a frame, fixture or enclosure, which may also be identifiedas a carrier. The carrier may be rigid or flexible and may providesupport for the lightsheet(s), an enclosure for the lightsheet(s),support for additional equipment such as a power supply, driver, controlor sense electronics, or the like.

In some embodiments, the lightsheet may include one or more conductiveelements on the back of the substrate, for example on the back ofsubstrate 165 illustrated in FIG. 1B. Such conductive elements, alsocalled power conductors, back power conductors, power bus, power buslines, and/or bus lines, may be configured and used to permit muchlonger lightsheets while still maintaining acceptable voltage loss inthe power conductor and thus acceptably high efficiency. FIGS. 9A and 9Bdepict an electrical device 900 in cross-section and plan viewrespectively. Electrical device 900 includes or consists essentially ofpower conductors 110, 120, conductive traces 160, strings 150, and LEEs130 formed over substrate 165. Electrical device 900 also features backpower conductors 910, 920 that are formed on the side of substrate 165opposite the side on which power conductors 110, 120 are formed. InFIGS. 9A and 9B, the CEs 140 are omitted for clarity. Back powerconductors 910, 920 may be electrically coupled to power conductors 110,120 respectively, using vias 930. Vias 930 permit electrical coupling ofback power conductor 910 to power conductor 110 and back power conductor920 to power conductor 120. Via 930 may include or consist essentiallyof, e.g., a crimp-type via or a through-hole that is been filled orpartially filled with conductive material 1050 (FIG. 10D). In someembodiments, a via 930 may have other configurations, for example aclamp 1010 (FIG. 10A), a rivet 1020 (FIG. 10B), a staple 1030 (FIG.10C), a wire, or the like. In some embodiments, the conductive tracesand/or power conductors are formed or printed and via 930 is formed aspart of the forming or printing process. The means of electricalcoupling between back power conductors 910, 920 and power conductors110, 120 is not a limitation of the present invention. In someembodiments, the connection between the back and front power conductorsmay be made by folding or rolling the end of the sheet, to put aconductor on one side of the sheet in contact with a conductor on theother side of the sheet, for example as shown in FIG. 10E, identified as1060 in FIG. 10E. In one embodiment, such a structure (shown in FIG.10E) may be held in place with tape, adhesive, a clamp, or other means.In some embodiments, via 930 may be formed in a roll-to-roll process. Insome embodiments, electrical coupling between back power conductors 910,920 and power conductors 110, 120 may be formed in the roll-to-rollprocess that is used to form the conductive elements (for example backpower conductors 910, 920, power conductors 110, 120 and/or conductiveelements 160) over substrate 165.

In some embodiments, the back and/or front metal may act as a reflectorfor light generated by LEEs 130, for example to direct it more in theforward direction, away from sheet 165. In some embodiments, conductiveelements 160, back power conductors 910, 920 and/or power conductors110, 120 may be reflective to a wavelength of light emitted by LEE 130.In some embodiments, conductive elements 160, back power conductors 910,920 and/or power conductors 110, 120 may have a reflectivity greaterthan 70% to a wavelength of light emitted by LEEs 130. In someembodiments, the conductive elements near or below LEEs 130 may beconfigured such that there is no direct pathway for light from the frontto the back of the lightsheet. One example of such a configuration isshown for electrical device 1100 in FIG. 11. While string 150 in FIGS.9B and 11 features five LEEs 130, this is not a limitation of thepresent invention, and in other embodiments string 150 may include orconsist essentially of any number of LEEs 130. In FIG. 11 CEs 140 areomitted for clarity.

In some embodiments of the present invention, the lightsheet may includeparallel groups of strings, as schematically illustrated in FIG. 12.This configuration permits manufacture of a lightsheet or lightsheet webwider than the length occupied by the string between adjacent powerconductors 110, 120. While FIG. 12 shows four adjacent strings, this isnot a limitation of the present invention and in other embodiments anynumber of strings may be configured adjacently in this fashion. WhileFIG. 12 shows strings 150 including four LEEs 130, this is not alimitation of the present invention and in other embodiments string 150may include any number of LEEs 130. FIG. 12 shows LEEs 130 oriented inopposite directions in adjacent groups of strings 150; however, this isnot a limitation of the present invention and the physical orientationof LEEs 130 may not be the same as in the electrical schematic. In otherembodiments, adjacent groups of strings 150 may be oriented in the samedirection and two sets of power conductors may be formed between eachgroup of strings, as shown in FIG. 13.

FIG. 14 shows a cross-sectional schematic of one embodiment of theelectrical schematic shown in FIG. 12 in accordance with this invention.In some embodiments, the sections of 120, 110 and 910, 920 adjacent tovia 930 are electrically continuous. While FIG. 14 shows four sectionsof strings 150, this is not a limitation of the present invention and inother embodiments any number of sections of strings may be used. In FIG.14, the sections of back power conductor 910 at the edges of sheet 165,identified in FIG. 14 as 910′, are not as wide as other 910 sections. Insome embodiments, back power conductors 910′ may have a width that isabout one-half the width of back power conductors 910. In someembodiments, back power conductors 910′ may carry about one half of thecurrent as other sections of back power conductors 910. In other words,in the electrical schematic shown in FIG. 12 back power conductors thatare electrically coupled to two sections of strings 150 carry abouttwice the current as back power conductors that are electrically coupledto one section of strings 150, and in some embodiments the resistance ofsuch strings that carry about twice the current may have about half ofthe resistance as back power conductors that carry the current for onesection of strings 150.

In some embodiments, control of the resistance may be by other meansthan controlling the width of the conductive traces, i.e., bycontrolling dimensions of conductive elements 160, power conductors 110,120, and/or back power conductors 910, 920. In some embodiments,resistance control may be achieved by using different thicknessconductive traces. In some embodiments, resistance control may beachieved by using different materials for different conductive traces ordifferent portions of conductive traces, for example with differentconductivities. In some embodiments, resistance control may be achievedby using a plurality of layers of conductive and/or non-conductivematerials that form all or portions of the conductive traces.

FIG. 15 illustrates an electronic device 1500 in accordance withembodiments of the present invention. Electronic device 1500 is similarto electronic device 900 of FIG. 9, but includes three segments 1540each containing multiple strings 150. In FIG. 15 CEs 140 are omitted forclarity. In some embodiments, the pitch between LEEs 130, identified as1510 in FIG. 15, is the same within a string segment 1540 (identified as1510′ in FIG. 15) as it is between string segments 1540. In other words,power conductors 110 and 120 have the same or substantially the samelength as conductive element 160. However, this is not a limitation ofthe present invention and in other embodiments, power conductors 110 and120 may have a length different from that of conductive element 160.

As shown in FIG. 15, the back power conductors 910, 910′, 920, 920′cover substantially all of the area of the back surface of substrate165. In some such embodiments, the resistance of the back powerconductors scales with the power required per unit length of thelightsheet. For example, In FIG. 15, the string length and distancebetween power conductors 110′ and 120 scales with the number of LEEs 130in the string (and thus the string voltage). The power per string is theproduct of the string voltage and current. Thus, as the string lengthincreases the power per string increases. For a fixed current drive,this means the string voltage increases. The resistance drop in the backpower conductor is the product of the current and voltage. For eachstring unit, this is just the product of the string voltage and thecurrent. If no change is made to the back power conductor resistance,the voltage drop in the back power conductor will increase withincreasing string length. However, by making the back power conductorcover essentially all of the area of the back of substrate 165, theresistance of the back power conductors scales inversely with the stringlength; that is, as the string length increases, the back powerconductor resistance per unit length decreases proportionately. The backpower conductor resistance in some embodiments may be defined by theproduct of the resistivity of the back power conductor material and itslength, divided by its cross-sectional area. As the width increases, thecross-sectional area increases and the resulting resistance decreases.Thus, the voltage drop per unit length of back power conductor is thesame for different string lengths. Therefore, from a design point ofview, once an acceptable back power conductor voltage or power loss perunit length has been determined, this same voltage or power loss perunit length is automatically maintained when the string length ordistance between front power conductors 110′ and 120 is changed.

As discussed above, the back power conductors that carry less currentare relatively narrower than the back power conductors that carry morecurrent. In the example shown in FIG. 15, the edge back powerconductors, identified as 910′ and 920′ carry current for one stringsegment 1540, while back power conductors 920 and 910 carry current fortwo string segments 1540. As shown, the width 1520 of back powerconductors 910′ or 920′ is about half the width 1530 of back powerconductors 910 and 920. However, this is not a limitation of the presentinvention and in other embodiments back power conductors 910, 910′, 920,920′ may all have the same width or different widths. While theexemplary embodiment shown in FIGS. 9A, 9B, 14, and 15 has the backpower conductors covering a large portion or substantially all of theback surface of substrate 165, this is not a limitation of the presentinvention and in other embodiments the back power conductors may cover asmaller portion of the back surface of substrate 165. In someembodiments, the back power conductors may be substantially the samesize as the front power conductors. In some embodiments, the back powerconductors may be substantially the same size as and positioned belowthe front power conductors, for example to achieve a more transparentlightsheet (i.e., to increase the amount of area of the lightsheet notcovered on one or both sides by a power conductor or conductive element160).

In some embodiments, the region between adjacent back power conductorsis shifted so that it does not coincide with the position of LEEs 130 onthe front of electronic device 1500. In some embodiments, thisconfiguration may provide relatively higher reflectivity from the backpower conductors to a wavelength of light emitted by LEEs 130.

As shown in FIG. 15, power conductors 120′ and 110′ that carry lesscurrent are relatively narrower than power conductors 110, 120 thatcarry more current. In the example shown in FIG. 15, the edge powerconductors, identified as 110′ and 120′ carry current for one stringsegment 1540, while power conductors 120 and 110 carry current for twostring segments 1540. As shown the width of power conductors 110′ or120′ is about one-half the width of power conductors 110 and 120.However, this is not a limitation of the present invention and in otherembodiments power conductors 110, 110′, 120, 120′ may all have the samewidth or different widths. FIG. 15 shows a larger number of vias 930 inwide power conductors (for example 110 and 910) than in the narrow powerconductors (for example 120′ and 920); however, this is not a limitationof the present invention and in other embodiments the number of vias 930in any given power conductor may be the same as or different from thatin other power conductors. In some embodiments, the number of vias 930in a particular power conductor may be proportional to the currentflowing in that power conductor, or to the conductivity of that powerconductor.

Utilization of the same electrical constraints as in the first exemplaryembodiment detailed above, that is V_(s)=60 V, V_(f)=3.0 V, and p=1 cm,results in a 20-LEE string having a “straight” string length of about 19cm. Thus, each string segment has a width of about 19 cm and thedistance between adjacent strings is about 1 cm. In this example, thelightsheet has three adjacent string segments—it thus looks similar toelectrical device 1500 shown in FIG. 15, but it has 20 LEEs 130 perstring instead of the five LEEs 130 per string shown in FIG. 15. Thus,the lightsheet in this example has a width of about 3×19=57 cm. If eachLEE 130 is operated at about 20 mA, then the amount of current requiredper string per cm is about 20 mA and the current required for the entiresheet per cm is 3×20=60 mA. Power conductor 120 has a width of about 0.9cm. Assuming power conductor 120 includes or consists essentially ofaluminum and has a sheet resistance of 0.04 ohm/sq for a 2.5 μmthickness, it has a resistance of about 0.044 ohm. Power conductor 120carries current for two string segments, and thus carries 120 mA perstring. Thus, the voltage drop in power conductor 120 per cm (or perstring) is about 0.0053 V, or a voltage drop per meter of 0.53 V, whichmay be unacceptably large. In particular, as the lightsheet lengthincreases, the voltage drop in the power conductor reduces the availablestring voltage down the length of the lightsheet away from the powersupply. At some point the available string voltage may not be sufficientto turn on LEEs 130 and operate CEs 140 in a string. This is in additionto power losses in the power conductors that may reduce luminousefficacy. By adding back power conductor 920, a relatively lowerresistance current path is added in parallel to power conductor 120. Forexample, if back power conductor 920 includes or consists essentially ofthe same material as power conductor 120, but has a width about sixtimes larger than that of power conductor 120, then its resistance andvoltage drop reduce proportionately to about 0.007 ohm/sq and about0.0009 V/cm, respectively.

In some embodiments, back power conductor 920 may include or consistessentially of a different material or set of materials with a lowersheet resistance, or may include or consist essentially of a thickerlayer of the same material as power conductor 120. This may result in afurther reduction in power conductor power loss. For example, back powerconductor 920 may have a thickness of at least about 10 μm or at leastabout 25 μm or at least about 50 μm or even larger than about 100 μm. Inthe case where back power conductor 920 has a thickness of about 25 μm,then the voltage drop per cm in the above example would be reduced by afactor of about 10 to about 0.00009 V per cm. In this case, a lightsheetmay be made 10 m long with a total voltage drop across back powerconductor 920 of only about 0.009 V. It should be noted that the powerlosses in the power conductors at the edge of the lightsheet are aboutthe same as the losses in the ones in the center, because the edge powerconductors have about half the width and thus about twice theresistance, but are carrying about one-half of the current. Thus in thisembodiment, the resistive losses are substantially equalized for bothsize power conductors.

This embodiment of the present invention therefore provides the abilityto make lightsheets with three key attributes: (i) very largedimensions, (ii) a single power connection to one end of the lightsheet,and (iii) relatively very low resistive power losses for relativelylarge lightsheet sizes. The width may be increased by adding additionaladjacent segments of strings while the length may be increased by addingmore strings between the power conductors. The pitch between LEEs 130 ina string is the same or substantially the same as between adjacent LEEs130 in adjacent strings and in adjacent string segments—that is, in boththe length and width direction of the lightsheet, resulting in theproduction of substantially uniform illumination from the sheet as afunction of area.

The discussion above provides one example of an embodiment of thepresent invention. The dimensions of and materials used for the powerconductors may be modified as discussed above to achieve acceptablepower losses and operation for a variety of lightsheet designs andsizes. For example, smaller lightsheet sizes may permit the use ofthinner power conductors or less costly materials making up the powerconductors, or may permit the elimination of the back power conductors.

Another embodiment of the present invention is a lightsheet orlightsheet web that may be manufactured in large area and then cut tosize. As discussed previously, cutting or segmentation of a lightsheetor lightsheet web may occur at various points in the manufacturingprocess. In some embodiments, lightsheets or lightsheet webs may beinventoried or stored in complete or partially completed form. In someembodiments, lightsheets or lightsheet webs may be segmented in thefield. In some embodiments, segmentation may occur after installation,for example to change the size of the lightsheet or to remove andreplace a damaged or nonfunctional lightsheet or portion of alightsheet.

Electrical device 1500 shown in FIG. 15 is one embodiment of aconfigurable lightsheet. In some embodiments, electrical device 1500 maybe manufactured on relatively large sheets or in rolls, for example in aroll-to-roll process. In an embodiment manufactured using roll-to-rollprocessing, lightsheet web 1500 may have a width for example of about500 mm, or about 1000 mm or larger. The width of lightsheet web 1500 isnot a limitation of the present invention. In an embodiment manufacturedusing roll-to-roll processing, lightsheet web 1500 may have a length forexample of about 100 m, or about 1000 m or about 10,000 m or larger. Thelength of lightsheet web 1500 is not a limitation of the presentinvention. Lightsheet web 1500 may be segmented or cut in both thelength and width directions. In the length direction, lightsheet web1500 may be cut or separated between strings 150, resulting in a minimumlength increment for lightsheet web 1500 shown in FIG. 15 of one string,which is basically equivalent to the LEE 130 pitch. In the example abovethis is 1 cm; however LEE 130 pitch is not a limitation of the presentinvention and in other embodiments LEE 130 pitch may have any value. Inthe width direction, lightsheet web 1500 may be cut or separated betweenstring segments, for example down the middle of power conductor 120 or110. This results in a minimum width increment for lightsheet web 1500shown in FIG. 15 of one string segment, which is basically equivalent tothe product of LEE 130 pitch and the number of LEEs 130 per string 150.In the example above, where the string voltage is 60 V, the number ofLEEs 130 per string is 20 and with a 1 cm LEE 130 pitch, this makes theminimum width increment about 19 cm. Thus in this example there isrelatively finer granularity of the length increment compared to widthincrement.

As shown in FIG. 15, there is not necessarily a one-to onecorrespondence between the number of vias 930 and the number of stringsin a lightsheet. In one embodiment of the present invention, each powerconductor has at least one via 930 for each string 150 attached to thatpower conductor, such that if lightsheet 1500 is cut or separatedbetween adjacent strings, each section has at least one via 930electrically coupling the back power conductor to the front powerconductor. However, this is not a limitation of the present inventionand in other embodiments the number of vias 930 in a given powerconductor may be more or less than the number of strings attached tothat power conductor. A plurality of vias 930 also provide redundancy;if one via 930 should fail open, the other vias 930 in that conductorcan still provide electrical conduction between the front and back withalmost no or little increase in resistance.

FIG. 15 also shows one embodiment of the orientation of LEEs 130. InFIG. 15, LEEs 130 in adjacent string segments are oriented in oppositedirections. For example in the string in the upper left-hand corner,power conductor 110′ provides a positive voltage to which the cathode ofLEE 130 is attached. At the end of this string the anode of the last LEE130 in the string is attached to the return, power conductor 120. In thestring just below this one, that is the one in the lower left-handcorner, the positions of LEEs 130 are reversed, such that the anode ofthe first LEE 130 is attached to power conductor 120 and the cathode ofthe last LEE 130 in the string is attached to power conductor 110.However, this is not a limitation of the present invention and in otherembodiments the orientation and electrical coupling of LEEs 130 may bedifferent.

FIG. 16 shows another embodiment of the present invention, electricaldevice 1600, which is similar to electrical device 1500 of FIG. 15;however, electrical device 1600 features folded strings. The orientationof LEEs 130 in each string segment is shown by the diode symbolsoverlaid on the schematic of electronic device 1600. The use of foldedstrings may be advantageous where the desired minimum increment inlightsheet web is less than the straight string length. Electricaldevice 1600 has multiple strings 150, where each string 150 comprises 18LEE 130 and a CE 140, and where the strings 150 are divided into twostring sections, also referred to as sections. Each string 150 ispowered via a connections to power conductor 110 on one end and powerconductor 120 on the other end. String segments are connected by powerconductors 1610 and 1620. Power conductors 110 and 120 have vias 930connecting them to back power conductors 910 and 920 respectively. InFIG. 16, back power conductor 920 is divided in half, so that there isno back power conductor 920 material in the region of cutline 1640. Insome embodiments, this may simplify separation or cutting of electricaldevice 1600. However, this is not a limitation of the present inventionand in other embodiments back power conductor 920 may not be divided inthis manner. The spacing between adjacent conductive elements 160 is nota limitation of the present invention. In some embodiments, the spacingmay be relatively larger, resulting in a relatively more narrowconductive element 160, while in other embodiments the spacing may berelatively smaller, resulting in a relatively wider conductive element160, for a fixed LEE 130 pitch. The example of FIG. 16 also shows thatin some embodiments CEs 140 may have any position within strings 150.While FIG. 16 shows one via 930 per power conductors 110 and 120 this isnot a limitation of the present invention and in other embodiments powerconductors 110 and 120 may have more than one via 930.

The schematic of electrical device 1600 may represent a stand-alonelightsheet, a portion of a stand-alone lightsheet, or all or a portionof a lightsheet web. As shown in FIG. 16, electrical device 1600 may becut or divided between strings 150 and/or between string sections.Cutline 1650 identifies one location between strings 150 whereelectrical device 1600 may be cut. In this embodiment, cut lines 1650are separated by a distance corresponding to about three times the pitchbetween LEEs 130, because each string 150 has three string segments. Inother embodiments, the number of string segments may have any value.Cutline 1640 identifies one possible location between string sectionswhere electrical device 1600 may be cut. In this embodiment, cut lines1640 are separated by a distance corresponding to about six times thepitch between LEE 130, because each string segment includes six LEEs130. In other embodiments, the number of LEEs per string segment mayhave any value. Using the example described above, where the LEE 130pitch is about 1 cm, this means the minimum size lightsheet is about 3cm long and about 6 cm wide. This defines a unit cell of lightsheet,shown as the grey area identified as 1660 in FIG. 16. As shown, LEEpitch 1630 is constant or substantially constant between adjacent LEEs130 whether they are in one string, in adjacent string segments, or inadjacent string sections.

This structure provides a useful advantage. Instead of having to designand manufacture lightsheets of many different shapes and sizes, alightsheet web may be manufactured in very large volumes and then cut tothe required sizes. Such cutting may be done during manufacture, aftermanufacture or in the field. In some embodiments, lightsheet web may beshipped to storage or distribution sites and cut to order. In someembodiments, lightsheet web may be shipped to a job site and cut toorder. The minimum lightsheet size is determined by unit cell 1660 size,as described above. The unit cell may be made relatively small,permitting relatively fine control of the final lightsheet size andshape. Using the values from the above example, the unit cell is about 3cm by about 6 cm, i.e., the minimum length increment is about 3 cm andthe minimum width increment is about 6 cm. In other embodiments, thenumber of LEEs 130 per string 150 and the configuration of string 150,for example a straight string, or how the string is folded, permitvariation of the size of unit cell 1660 and thus of the minimum lengthand width increments.

Just as electrical device 1600 may be cut or separated into unit cellsegments, multiple segments or lightsheets may be tiled together in thelength or width or both length and width directions without any changein pitch across the joint between adjacent segments or lightsheets. Thispermits fabrication, both at the manufacture site, and in the field, ofrelatively large illuminated areas comprising multiple lightsheets, withno change in LEE 130 pitch or optical characteristics across the joint.

FIG. 17 shows another embodiment of the present invention, electricaldevice 1700, which is similar to electrical device 1600 shown in FIG.16; however, in the case of electrical device 1700, each string 150includes one or more string segments that do not comprise LEEs 130. Asindicated by the diode symbols overlaid on the schematic of electronicdevice 1700, this permits all LEEs 130 to have the same orientation inall string segments, in contrast to electrical device 1600 shown in FIG.16. Furthermore, the back power conductors in electrical device 1700have been positioned such that all LEEs 130 in the different stringsegments have the same orientation. In some embodiments, this maysimplify the positioning and formation of LEEs 130 on substrate 165.

In some embodiments of the present invention, all or portions of thefront and/or back of the lightsheet may be covered by a cover layer ormaterial. In some embodiments, the cover layer may include or consistessentially of an insulating layer, for example to prevent electricalcontact with conductive elements 160, power conductors 110, 120 and/orback power conductors 910, 920. In some embodiments, the insulatingmaterial may include or consist essentially of, e.g., one or more layersformed over the back or front. Such layers may include or consistessentially of a material the same as or similar to that of substrate165, e.g., PET, PEN, polyimide, polyester, acrylic or the like. In someembodiments, the insulating material may include or consist essentiallyof, for example, silicone, silicon oxide, silicon dioxide, siliconnitride or the like. In some embodiments, the insulating material maycomprise an ink, where the ink may have one or a plurality of colors ormarkings. In some embodiments the insulating material comprises a whiteink. In some embodiments, the insulating material may be a separatelayer adhered to the lightsheet, for example using glue or adhesive ortape. In some embodiments, the insulating material may be formed overthe lightsheet by, for example, spray coating, dip coating, printing,sputtering, evaporation, chemical vapor deposition or the like. In someembodiments, the insulating layer may be patterned and a portion of theinsulating layer removed to permit access to a portion of the underlyinglightsheet. In some embodiments, the insulating layer may be patternedsuch that it does not cover LEEs 130. In some embodiments, patterningmay be achieved by selective deposition, for example, selective spraycoating, or by patterning and etching or removal of portions of theinsulating layer. In some embodiments, the cover layer may haveadditional properties, for example, to provide flame resistance or toprovide a reflective or light-absorbing surface. In some embodiments, afront cover material is reflective to a wavelength of light emitted byLEEs 130. In some embodiments, the front cover material is white. Insome embodiments, the back cover layer is black.

FIG. 18 is a cross-section of an exemplary electrical device 1800.Electrical device 1800 features a back cover layer 1810 and a frontcover layer 1820. In the embodiment shown in FIG. 18, back cover layer1810 covers the entire backside of electrical device 1800; however, thisis not a limitation of the present invention and in other embodimentsportions of the backside of electrical device 1800 may be exposed. Inthe embodiment shown in FIG. 18, front cover layer 1820 covers portionsof electrical device 1800, leaving LEEs 130 as well as a portion 1830 ofa power conductor 110 exposed. Portion 1830 of power conductor 110 maybe used, for example, to provide electrical coupling to electricaldevice 1800. However, this is not a limitation of the present invention,and in other embodiments all of the front of electrical device may becovered by front cover layer 1820. In some embodiments all or a portionof LEEs 130 may be covered by front layer 1820. In some embodiments,electrical connection to electrical device 1820 may be made by piercingor scraping away a portion of front cover layer 1820 and/or back coverlayer 1810. In some embodiments, such removal of portions of the coverlayers may occur during application of a connector or wire or othermeans of electrical connection to electrical device 1800. In someembodiments, the front and/or back cover layers are formed using printedink. In some embodiments, the front cover layer includes or consistsessentially of white ink. In some embodiments, the back cover layerincludes or consists essentially of black ink. Each lightsheet may beelectrically coupled to a power source or to an adjacent lightsheet. Inone embodiment, a first set of power conductors 110, 120 on a firstlightsheet are electrically coupled to a second set of power conductors110, 120 on a second lightsheet. Forming an electrical connection to apower conductor on a lightsheet may be done using a variety oftechniques; the means of electrical connection is not a limitation ofthe present invention. In one embodiment, electrical connection to apower conductor on a lightsheet is made using a crimp connector 1910(where the crimp connector is pressed against power conductor 110 andsubstrate 165 such that it makes an electrical connection), as shown inFIG. 19. The crimp connector 1910 may be electrically coupled to a wire1920, wiring harness, printed circuit board or the like. In oneembodiment, crimp connector 1910 includes or consists essentially of acrimp connector such as an Etco crimp part number 51608.

One or more lightsheets may be powered from a power supply, for examplea constant-voltage or constant-current power supply. In someembodiments, the input power for the power supply may be line voltage,for example 120 AC, 240 VAC, 277 VAC with a frequency of, for example,50 Hz or 60 Hz. In some embodiments, the power supply may include orconsist essentially of a universal power supply capable of accommodatinga relatively wide range of input voltages and frequencies. In someembodiments, the input power for the power supply may be a DC voltage.The input power for the power supply is not a limitation of the presentinvention and in other embodiments any input power may be used.

FIG. 20 is a schematic of an exemplary lighting system in accordancewith embodiments of the present invention and that includes or consistsessentially of a power supply 2030 with input power 2040, and one ormore lightsheets 360, where power supply 2030 has an output 2050 thatoptionally may split into two conductors 2051 and 2052 that areelectrically coupled to power conductors 110 and 120 respectively. Insome embodiments, an advantage of this approach is that one power supply2030 may provide power to one or more lightsheets, independent of thenumber of strings 150 on the lightsheet and/or independent of the numberof lightsheets electrically connected in series. In some embodiments,the power capacity of power supply 2030 may be varied to match that ofdifferent lightsheets. For example, in some embodiments, lightsheet 360may have 40 strings, each string operating at nominally 5 mA. In thisexample each lightsheet utilizes about 200 mA of current. If theconstant voltage is about 60 volts, then the lightsheet utilizes about12 watts. If one lightsheet is connected to the power supply, then thepower supply should provide at least 12 watts. If two lightsheet areconnected to the power supply in series, then the power supply shouldprovide at least 24 watts. In this way it is relatively straightforwardto determine the power levels required to support any one or combinationof lightsheets. In some embodiments, one or a small number of powersupplies may be able to provide power to a relatively large number ofconfigurations of lightsheets, thus advantageously reducing the numberof power supplies required to be manufactured and/or stocked.

FIGS. 21A and 21B show other exemplary embodiments of lighting systemsin accordance with embodiments of the present invention that include orconsist essentially of power supply 2030 with input power 2040, and oneor more lightsheets 360. In FIG. 21A lightsheets 360 are in a seriesconfiguration, while in FIG. 21B lightsheets 360 are in a parallelconfiguration. While the examples shown in FIGS. 20, 21A, and 21B depicttwo lightsheets 360, this is not a limitation of the present inventionand in other embodiments the lighting system may include one lightsheet360 or more than two lightsheets 360. While the examples shown in FIGS.20, 21A, and 21B show one power supply 2030, this is not a limitation ofthe present invention and in other embodiments the lighting system mayfeature multiple power supplies 2030. While the examples shown in FIGS.20, 21A, and 21B show the lightsheets 360 electrically coupled byadditional conductors, for example 2010 and 2020 in FIG. 20 or 2010 inFIG. 21A, this is not a limitation of the present invention and in otherembodiments multiple lightsheets 360 are tiled together, as describedabove, and electrically coupled together without the use of additionalwires. In such embodiments a variety of means of electrical coupling maybe used, for example including crimp connectors, ZIF connectors, edgeconnectors, electrically coupling rivets or staples, conductiveadhesives or glues, conductive tapes, adhesives, glues, tapes, or thelike.

In some embodiments, the light intensity or light output power of thelighting system, for example as shown in FIGS. 20, 21A, and 21B, may beadjustable or may be dimmed. In one embodiment, the light output powerof the lighting system may be adjusted by modulating the output powerfrom power supply 2030. In one embodiment, the light output power of thelighting system may be adjusted by pulse width modulating the outputpower from power supply 2030.

In some embodiments, LEEs 130 of one or more lightsheets are of the sametype. In some embodiments, LEEs 130 of one or more lightsheets may bedifferent. In some embodiments, the lightsheet may include multipledifferent types of LEEs 130. For example, different types of LEEs 130may include different size LEEs 130 or LEEs 130 that have differentelectrical or optical characteristics, such as emission wavelength,forward voltage, and/or spectral power distribution. In someembodiments, a string 150 may include multiple LEEs 130 of the sametype; however, this is not a limitation of the present invention and inother embodiments the string 150 may include more than one type of LEE,for example LEEs that emit light at different wavelengths or withdifferent spectral power distributions or have different sizes. In someembodiments, the lightsheet may include multiple strings 150, where eachstring 150 includes or consists essentially of multiple LEEs 130 of thesame type; however, this is not a limitation of the present inventionand in other embodiments the lightsheet many include multiple strings150 where each string 150 may include or consist essentially of morethan one type of LEE, for example LEEs that emit light at differentwavelengths or with different spectral power distributions or havedifferent sizes. The number of different types of LEEs 130 orlightsheets of a lighting system is not a limitation of the presentinvention. The number of different types of lightsheets of the lightingsystem is not a limitation of the present invention. In someembodiments, the lighting system may include a combination of bare-dieLEEs 130 and packaged LEDs 130.

In some embodiments, a lightsheet, lightsheet web or lightsheet-basedillumination system may also include one or more control elements thatpermit control of LEEs 130 within a string 150, individual strings 150and/or one or more groups of strings 150. Such control may beimplemented within one lightsheet or group of lightsheets, for example,lightsheets that are tiled together. These control elements may be usedfor a variety of purposes. For example, in some embodiments, strings maybe individually or group-wise addressed and controlled to provide arange of light levels, for example to implement dimming functionality.In one embodiment, this may be implemented by turning one or morestrings off to reduce the overall light output level. In one embodimentthis may be implemented by changing the drive current level to LEEs 130within one or more strings 150. In one embodiment this may beimplemented by pulse-width-modulating the power, e.g., the current orvoltage, to LEEs 130 within one or more strings 150.

In some embodiments, different strings 150 may include one or moredifferent types of LEEs 130, for example, having different colortemperatures or light distribution patterns. In this way one or moreoptical characteristics of the lightsheet or illumination system may bechanged by selective activation and deactivation of one or groups ofstrings 150, or by changing the drive current to one or more groups ofstrings 150.

FIG. 22A shows another embodiment of the present invention, similar tothat shown in FIG. 20; however the embodiment in FIG. 22A featurescontrol input 2210 and control channel 2220. In some embodiments,control input 2210 and control channel 2220 may be used to control oneor more characteristics of lightsheets 360, for example light intensity,dimming, color temperature, light distribution pattern, or the like. Insome embodiments, control input 2210 and control channel 2220 may beused to selectively address and activate and deactivate one or morestrings 150 or lightsheets 360. For example, a lightsheet 360 maycomprise a plurality of strings or a plurality of groups of strings 150,where each string has LEEs 130 with different characteristics, forexample light output power, color temperature, color rendering index,light distribution patterns or the like, and control input 2210 andcontrol channel 2220 may be used to selectively activate, deactivate, orpartially power one or more strings 150 or groups of strings 150.

In some embodiments, control input 2210 may be applied to power supply2030 as shown in FIG. 22A; however, this is not a limitation of thepresent invention and in other embodiments control input 2210 may beapplied directly to lightsheets 360 or may be applied to lightsheets 360through power supply 2030 or one or more intermediate systems (notshown). In some embodiments, control input 2210 and control channel 2220may comprise one conductor, while in other embodiments control input2210 and control channel 2220 may comprise a plurality of conductors. Insome embodiments, control input 2210 and control channel 2220 may carryone signal, while in other embodiments control input 2210 and controlchannel 2220 may carry a plurality of signals. In some embodiments,control input 2210 and control channel 2220 may act on or control allstrings 150 within one or more lightsheets 360 simultaneously, while inother embodiments control input 2210 and control channel 2220 mayindependently control each or a plurality of strings 150 within one ormore lightsheets 360. In some embodiments, each lightsheet 360 and/oreach string 150 may be separately identifiable or addressed so as topermit individual control of each lightsheet 360 and/or each string 150.

FIG. 22B is a schematic of a lightsheet or a portion of a lightsheethaving two groups of strings 150, identified as 150 and 150′. Controlelements 140 are associated with strings 150 and have an address A,while control elements 140 associated with strings 150′ are identifiedas 140′ and have an address B. In one embodiment, strings 150 and 150′have different optical characteristics, for example color temperature,CRI, light output power, or the like. In one embodiment, control channel2220 provides a signal that addresses strings 150 and 150′ separately,telling each group when to activate and when to deactivate. In oneembodiment, the drive currents to strings 150 and/or 150′ are fixed andcontrol channel 2220 only acts to activate or deactivate the strings. Inone embodiment, control channel 2220 carries information related todrive current, and thus is able to not only activate or deactivategroups of strings 150 and 150′, but to independently change the drivecurrent to groups of strings 150 and 150′. In one embodiment, controlchannel 2220 carries information related to the power to LEEs 130, andthus is able to not only activate or deactivate groups of strings 150and 150′, but also to independently change the power to groups ofstrings 150 and 150′, e.g., by modulation of the voltage and/or current.In some embodiments, each string 150 has its own address and thus isable to be controlled independently of all other strings 150. In someembodiments, a lighting system may comprise a plurality of lightsheets,where each lightsheet has a plurality of groups of independentlyaddressable and controllable strings. In some embodiments, the pluralityof groups of independently addressable and controllable strings are thesame on each of the plurality of lightsheets in the system, while inother embodiments the groups of independently addressable andcontrollable strings are different on one or more of the plurality oflightsheets in the system,

FIG. 23 is a schematic of an electrical device 2300 that includescontrol channels 2220 and 2220′ that are formed on the back ofelectrical device 2300 and are electrically coupled to control elements140 through vias 930. In some embodiments, control channel 2220 and2220′ may be the same, while in other embodiments control channel 2220and control channel 2220′ may be different. While FIG. 23 shows twocontrol channels 2220, this is not a limitation of the present inventionand in other embodiments electrical device 2300 may feature more thantwo control channels 2220. While FIG. 23 shows control channels 2220 onthe back of electrical device 2300, this is not a limitation of thepresent invention and in other embodiments control channels may be onthe front of electrical device 2300 or may be on both the back and frontof electrical device 2300.

FIG. 24 shows an example of an embodiment of the present invention thatfeatures strings 150 electrically coupled to power conductors 110 and120 and a control element 2440 that comprises multiple control elements140. In some embodiments, control element 2440 may comprise multiplecontrol elements 140 integrated in a monolithic or hybrid form on one ora plurality of semiconductor chips. In some embodiments the structureshown in FIG. 24 may optionally include control input 2210 and/orcontrol channel 2220. In some embodiments, control element 2440 mayinclude additional circuitry to permit addressing or control of strings150.

As described above, lightsheet 360 may have conductive traces on thefront, back or both sides. In some embodiments, it may be desirable tohave separate conductive traces cross each other without electricalcoupling between the two conductive traces but not have conductivetraces on both sides of lightsheet 360. In this case cross-over elementsmay be employed as shown in FIGS. 25A and 25B, which depict a crossoverelement 2550 that electrically couples conductive elements 160 and 160′together and bridges conductive element 160″. Conductive element 2550may include a base 2520 over which is formed a conductive layer 2510 andoptional pads 2530. In other embodiments, conductive element 2550 may beformed of a single conductive material. In some embodiments, base 2520may be insulating, and may therefore include or consist essentially of,for example, sapphire, glass, plastic, or the like. In some embodiments,base 2520 may include or consist essentially of a semiconductor such assilicon, gallium arsenide, gallium phosphide, or the like. In someembodiments, conductive layer 2510 may include or consist essentially ofone or more metals such as silver, copper, gold, aluminum, chromium,tungsten, titanium, or the like. The specific configuration ofconductive element 2550 is not a limitation of the present invention. Insome embodiments pads 2530 may be bond pads or stud bumps. In someembodiments, pads 2530 may include or consist essentially of one or moreconductive materials, e.g., metals such as gold.

While the discussion above related to control signals has used controllines on the lightsheet to deliver the control signals to the controlelements, this is not a limitation of the present invention and in otherembodiments control signals may be delivered to control elements by anymeans, for example using light-based communication, radio-basedcommunication, Wi-Fi, or communication using radiation in other parts ofthe electromagnetic spectrum.

While the discussion above has focused on one-way control, that is theuse of control signals to effect changes on the lightsheet, this is nota limitation of the present invention and in other embodimentscommunication may be bidirectional. For example, in some embodimentsLEEs, 130, strings 150, or the lightsheet may communicate informationback to a control system. Examples of such information may includelightsheet or LEE 130 temperature, light output value, operation time,lumen degradation, color temperature, or the like.

Control input 2210 may be provided in a variety of ways. In oneembodiment, control input 2210 may be provided from a switch or knobthat is actuated manually. In one embodiment, control input 2210 mayoriginate from another system, for example, one that is used to controllighting within the space. In one embodiment, control input 2210 mayoriginate in a building management system, for example, one thatcontrols heating or lighting or emergency operations or the like. In oneembodiment, control input 2210 may originate in a portable or wirelessdevice, for example a mobile phone, computer, tablet, or the like. Inone embodiment, control input 2210 may originate from a sensor system,for example, one that senses ambient light, occupancy, heat, humidity,smoke or the like. In one embodiment, sensors that act to providecontrol input 2210 may be positioned on the lightsheet or within theluminaire containing the lightsheet or they may be positioned elsewhere.

While the discussion above related to control signals has used controllines on the lightsheet to deliver the control signals to the controlelements to control aspects of the lightsheet, this is not a limitationof the present invention and in other embodiments control signals may beprovided for other purposes, for example, to act as a receiving andtransmitting center for wireless signals for tablets, computers,telephones, mobile phones and other such electronic devices. Suchcommunication signals may take place over any portion of theelectromagnetic spectrum, for example IR, visible light, UV, radiowaves, etc.

As utilized herein, the term “light-emitting element” (LEE) refers toany device that emits electromagnetic radiation within a wavelengthregime of interest, for example, visible, infrared or ultravioletregime, when activated, by applying a potential difference across thedevice or passing a current through the device. Examples oflight-emitting elements include solid-state, organic, polymer,phosphor-coated or high-flux LEDs, laser diodes or other similar devicesas would be readily understood. The emitted radiation of an LEE may bevisible, such as red, blue or green, or invisible, such as infrared orultraviolet. An LEE may produce radiation of a continuous ordiscontinuous spread of wavelengths. An LEE may feature a phosphorescentor fluorescent material, also known as a light-conversion material, forconverting a portion of its emissions from one set of wavelengths toanother. In some embodiments, the light from an LEE includes or consistsessentially of a combination of light directly emitted by the LEE andlight emitted by an adjacent or surrounding light-conversion material.An LEE may include multiple LEEs, each emitting essentially the same ordifferent wavelengths. In some embodiments, a LEE is an LED that mayfeature a reflector over all or a portion of its surface upon whichelectrical contacts are positioned. The reflector may also be formedover all or a portion of the contacts themselves. In some embodiments,the contacts are themselves reflective. Herein “reflective” is definedas having a reflectivity greater than 65% for a wavelength of lightemitted by the LEE on which the contacts are disposed. In someembodiments, an LEE may include or consist essentially of an electronicdevice or circuit or a passive device or circuit. In some embodiments,an LEE includes or consists essentially of multiple devices, for examplean LED and a Zener diode for static-electricity protection. In someembodiments, an LEE may include or consist essentially of a packagedLED, i.e., a bare LED die encased or partially encased in a package. Insome embodiments, the packaged LED may also include a light-conversionmaterial. In some embodiments, the light from the LEE may include orconsist essentially of light emitted only by the light-conversionmaterial, while in other embodiments the light from the LEE may includeor consist essentially of a combination of light emitted from an LED andfrom the light-conversion material. In some embodiments, the light fromthe LEE may include or consist essentially of light emitted only by anLED.

One or more non-LEE devices such as Zener diodes, transient voltagesuppressors (TVSs), varistors, etc., may be placed on each lightsheet toprotect the LEEs 130 from damage that may be caused by high-voltageevents, such as electrostatic discharge (ESD) or lightning strikes. Inone embodiment, conductive trace segments shown in FIG. 1B between theLEE strings 150 may be used for placement of a single protection deviceper lightsheet, where the device spans the positive and negative powertraces, for example power conductors 110, 120. These trace segments alsoserve to provide a uniform visual pattern of lines in the web direction,which may be more aesthetically pleasing than a lightsheet withnoticeable gaps between LEE strings 150. In a more general sense, inaddition to conductive traces 160 that are part of string 150,additional conductive traces 160 that may or may not be electricallycoupled to other strings 150 and/or power conductors 110, 120 may beformed on substrate 165, for example to provide additional powerconduction pathways or to achieve a decorative or aesthetically pleasinglook to the pattern on the lightsheet or to provide a communicationpathway to one or more CEs 140, for example to provide a control signalto the one or more CEs 140. These trace segments also serve to provide auniform visual pattern of lines in the web direction, which may be moreaesthetically pleasing than a lightsheet with noticeable gaps betweenLEE strings 150.

In one embodiment, an LEE 130 includes or consists essentially of a baresemiconductor die 2600, a schematic example of which is shown in FIG.26, which may include a substrate 2610 with one or more semiconductorlayers 2620 disposed thereover. In an exemplary embodiment, LEE 130represents an LEE such as an LED or a laser, but other embodiments ofthe invention feature one or more semiconductor dies with different oradditional functionality, e.g., processors, sensors, detectors,photovoltaic cells, control elements, and the like. Non-LEE dies may ormay not be bonded as described herein, and may or may not have contactgeometries differing from those of the LEEs; moreover, they may or maynot have semiconductor layers disposed over a substrate as discussedbelow. Substrate 2610 may include or consist essentially of one or moresemiconductor materials, e.g., silicon, GaAs, InP, GaN, and may be dopedor substantially undoped (e.g., not intentionally doped). In someembodiments, substrate 2610 includes or consists essentially of sapphireor silicon carbide; however, the composition of the substrate is not alimitation of the present invention. Substrate 2610 may be substantiallytransparent to a wavelength of light emitted by the LEE 130 and/orlight-conversion material 2710 (see FIG. 27). The semiconductor layers2620 may include or consist essentially of first and second doped layers2630, 2650 that are preferably doped with opposite polarities (i.e., onen-type doped and the other p-type doped). One or more light-emittinglayers, e.g., or one or more quantum wells 2640, may be disposed betweenlayers 2630 and 2650. Each of layers may include or consist essentiallyof one or more semiconductor materials, e.g., silicon, InAs, AlAs, GaAs,InP, AlP, GaP, InSb, GaSb, AlSb, GaN, AlN, InN, and/or mixtures andalloys (e.g., ternary or quaternary, etc. alloys) thereof. In preferredembodiments, LEE 130 is an inorganic, rather than a polymeric ororganic, device.

As used herein, wavelength-conversion material or phosphor refers to anymaterial that shifts the wavelengths of light irradiating it and/or thatis fluorescent and/or phosphorescent, is utilized interchangeably withthe terms “light-conversion material” or “phosphor,” and may refer toonly a powder or particles or to the powder or particles with a binder.In some embodiments, the phosphor includes or consists essentially of amixture of one or more wavelength-conversion materials and a matrixmaterial. The wavelength-conversion material is incorporated to shiftone or more wavelengths of at least a portion of the light emitted bythe light emitter to other desired wavelengths (which are then emittedfrom the larger device alone or color-mixed with another portion of theoriginal light emitted by the die). A wavelength-conversion material mayinclude or consist essentially of phosphor powders, quantum dots or thelike within a transparent matrix. Phosphors are typically available inthe form of powders or particles, and in such case may be mixed inbinders, e.g., silicone. Phosphors vary in composition, and may includelutetium aluminum garnet (LuAG or GAL), yttrium aluminum garnet (YAG) orother phosphors known in the art. GAL, LuAG, YAG and other materials maybe doped with various materials including for example Ce, Eu, etc. Thephosphor may be a plurality of individual phosphors. The specificcomponents and/or formulation of the phosphor and/or matrix material arenot limitations of the present invention.

The binder may also be referred to as an encapsulant or a matrixmaterial. In one embodiment the binder includes or consists essentiallyof a transparent material, for example a silicone-based material orepoxy, having an index of refraction greater than 1.35. In oneembodiment, the phosphor includes other materials, for example SiO₂,Al₂O₃, fumed silica or fumed alumina, to achieve other properties, forexample to scatter light, to change the viscosity or to reduce settlingof the powder in the binder. An example of the binder material includesmaterials from the ASP series of silicone phenyls manufactured by ShinEtsu, or the Sylgard series manufactured by Dow Corning.

In some embodiments, substantially all or a portion of substrate 2610 isremoved prior to or after the bonding of LEE 130 described below. Suchremoval may be performed by, e.g., chemical etching, laser lift-off,mechanical grinding and/or chemical-mechanical polishing or the like. Insome embodiments all or a portion of substrate 2610 is removed and asecond substrate—e.g., one that is transparent to or reflective of awavelength of light emitted by LEE 130—is attached to the substrate orsemiconductor layer 2620 prior to or after the bonding of LEE 130 asdescribed below. In some embodiments substrate 2610 includes or consistsessentially of silicon and all or a portion of the silicon substrate maybe removed prior to or after the bonding of LEE 130 described below.Such removal may be performed by, e.g., chemical etching, laser liftoff, mechanical grinding and/or chemical-mechanical polishing or thelike.

Electrical contact to LEE 130 may be achieved through contacts 2670 and2680, which may make contact to the p- and n-layers 2650, 2630respectively. LEE 130 may optionally feature a minor or reflectivesurface 2660 formed over all or portions of layer 2650 and optionallyother portions of LEE 130. Mirror 2660 may act to direct light emittedfrom light-emitting layer 2640 back towards and out of the substrate2610, particularly in a flip-chip configuration where LEE 130 is mountedcontact side down.

In some embodiments, LEE 130 has a square shape, while in otherembodiments LEE 130 has a rectangular shape. In some preferredembodiments, to facilitate bonding (as described below) LEE 130 has ashape with a dimension in one direction that exceeds a dimension in anorthogonal direction (e.g., a rectangular shape), and has an aspectratio of the orthogonal directions (length to width, in the case of arectangular shape) of LEE 130 greater than about 1.2:1. In someembodiments, LEE 130 has an aspect ratio greater than about 2:1 orgreater than 3:1. The shape and aspect ratio are not critical to thepresent invention, however, and LEE 130 may have any desired shape.

In some embodiments, LEE 130 has one lateral dimension less than 500 μm.Exemplary sizes of semiconductor die 2610 may include about 250 μm byabout 600 μm, about 250 μm by about 400 μm, about 250 μm by about 300μm, or about 225 μm by about 175 μm. In some embodiments, LEE 130includes or consists essentially of a small LED die, also referred to asa “microLED.” A microLED generally has one lateral dimension less thanabout 300 μm. In some embodiments, semiconductor die 2610 has onelateral dimension less than about 200 μm or even less than about 100 μm.For example, a microLED may have a size of about 225 μm by about 175 μmor about 150 μm by about 100 μm or about 150 μm by about 50 μm. In someembodiments, the surface area of the top surface of a microLED is lessthan 50,000 μm² or less than 10,000 μm². However, the size of LEE 130 isnot a limitation of the present invention and in other embodiments LEE130 may have any size. For example, in some embodiments LEE 130 may haveone lateral dimension of about 1 mm or about 2 mm. In some embodiments,LEE may include or consist essentially of a relatively large high-powerpackaged LEE, for example a relatively large high-power LED, for examplewith an input power of about 1 W, about 3 W, or 10 W or larger.

In some embodiments, LEE 130 may include or consist essentially of a“white die” that includes an LED that is integrated with alight-conversion material (e.g., a phosphor) before being attached tothe lightsheet. An exemplary schematic of a white die 2700 is shown inFIG. 27. As shown, white die 2700 includes a die 2720 that is partiallycovered or encased in a light-conversion material 2710. All or portionsof contacts 2670, 2680 may be exposed to provide for electrical contactto die 2720. In some embodiments die 2720 is a bare LED, such as thatshown and described in reference to FIG. 26.

In some embodiments, white die 2700 is formed by forming thelight-conversion material 2710 over and/or around multiple dies 2720 andthen separating this structure into individual white dies as shown inFIG. 27 and as described in U.S. Provisional Patent Application No.61/589,908, filed Jan. 24, 2012, the entire disclosure of which isincorporated by reference herein. FIG. 27 depicts one die 2720associated with light-conversion material 2710, but this is not alimitation of the present invention and in other embodiments multipledies 2720 are associated with the same surrounding light-conversionmaterial 2710. FIG. 27 shows light-conversion material 2710 having asquare or rectangular shape; however, this is not a limitation of thepresent invention and in other embodiments light-conversion material2710 has a hemispherical or substantially hemispherical shape, aparabolic or substantially parabolic shape, or any shape. FIG. 27 showssubstantially the same thickness of light-conversion material 2710 overthe top and sidewalls of die 2720; however, this is not a limitation ofthe present invention and in other embodiments the thickness oflight-conversion material 2710 varies over different portions of die2720. White die 2700 may be used to produce embodiments of thisinvention, rather than forming a light-conversion material 2710 over die2720 after attachment of die 2720 to substrate 165.

Light-conversion material 2710 may include or consist essentially of atransparent binder material alone, or phosphor powders, quantum dots orthe like within a transparent binder matrix. Phosphors vary incomposition, and in some embodiments may include lutetium aluminumgarnet (LuAG or GAL), yttrium aluminum garnet (YAG) or other phosphorsknown in the art. GAL, LuAG, YAG and other materials may be doped withvarious materials including for example Ce, Eu, silicates doped withvarious materials including Ce, Eu, etc., aluminates, nitrides, and thelike. The specific components and/or formulation of the phosphor and/ormatrix material are not limitations of the present invention.

Light-conversion material 2710 may include a combination of individualphosphors. In one embodiment, the transparent matrix or binder includessilicone, epoxy, or other suitable materials. An example of a matrixmaterial includes materials from the ASP series of silicone phenylsmanufactured by Shin Etsu, or the Sylgard series manufactured by DowCorning. The specific components and/or formulation of the phosphorand/or matrix material are not limitations of the present invention.

It should be noted that LEEs 130 may have other features than thoseshown in FIG. 26 or 27 or discussed above, or may have fewer or morefeatures than shown in FIG. 26 or 27 or discussed above; the details ofLEEs 130 are not limiting to the present invention.

In another embodiment, an LEE 130 includes or consists essentially of apackaged semiconductor die, for example a packaged laser diode or LED.FIG. 28 shows an exemplary packaged LED 2800 that includes a die 2720having contacts 2670, 2680 that are electrically coupled to packagecontacts 2870, 2880 respectively. A package body 2810 holds or encasesall or a portion of the die 2720. All or a portion of the interior ofpackage body 2810 may be empty, or may be filled with a material 2830,which may include or consist essentially of a transparent material suchas a binder (for example silicone or epoxy), or a light-conversionmaterial, such as one or more phosphors or similar materials infused ina binder. In some embodiments the binder may have an index of refractiongreater than about 1.35 or greater than about 1.45. Contacts 2670, 2680may be electrically coupled to package contacts 2870, 2880 respectivelyusing a variety of techniques, for example wire bonding, ball bonding,solder, conductive adhesive, anisotropic conductive adhesive (ACA) orthe like. Packaged LEE 2800 shown in FIG. 28 is an example of one typeof packaged LEE. As is known to those skilled in the art, many differenttypes of packaged LEEs are available, and the type or size of packagedLEE is not a limitation of the present invention.

In some embodiments, LEEs 130 may emit light in a relatively smallwavelength range, for example having a full width at half maximum in therange of about 20 nm to about 200 nm. In some embodiments, all LEEs 130may emit light of the same or substantially the same wavelength, whilein other embodiments different LEEs 130 may emit light of differentwavelengths. In some embodiments LEEs 130 may emit white light, forexample that is perceived as white light by the eye. In someembodiments, the white light may be visible light with a spectral powerdistribution the chromaticity of which is close to the blackbody locusin the CIE 1931 xy or similar color space. In some embodiments, whitelight has a color temperature in the range of about 2000 K to about10,000 K. The emission wavelength, full width at half maximum (FWHM) ofthe emitted light or radiation or other optical characteristics of LEEs130 may not be all the same and are not a limitation of the presentinvention.

Substrate 165 may include or consist essentially of a semicrystalline oramorphous material, e.g., polyethylene naphthalate (PEN), polyethyleneterephthalate (PET), polycarbonate, polyethersulfone, polyester,polyimide, polyethylene, fiberglass, FR4, MCPCB, and/or paper. Substrate165 may include multiple layers, e.g., a deformable layer over a rigidlayer, for example, a semicrystalline or amorphous material, e.g., PEN,PET, polycarbonate, polyethersulfone, polyester, polyimide,polyethylene, and/or paper formed over a rigid substrate for examplecomprising, acrylic, aluminum, steel and the like. Depending upon thedesired application for which embodiments of the invention are utilized,substrate 165 may be substantially optically transparent, translucent,or opaque. For example, substrate 165 may exhibit a transmittance or areflectivity greater than 70% for optical wavelengths ranging betweenapproximately 400 nm and approximately 700 nm. In some embodimentssubstrate 165 may exhibit a transmittance or a reflectivity of greaterthan 70% for one or more wavelengths emitted by LED 130. Substrate 165may also be substantially insulating, and may have an electricalresistivity greater than approximately 100 ohm-cm, greater thanapproximately 1×10⁶ ohm-cm, or even greater than approximately 1×10¹⁰ohm-cm.

Conductive elements, i.e., power conductors 110, 120, back powerconductors 910, 920 and conductive traces 160, may be formed viaconventional deposition, photolithography, and etching processes,plating processes, lamination, lamination and patterning, evaporationsputtering or the like or may be formed using a variety of differentprinting processes. For example, power conductors 110, 120, back powerconductors 910, 920 and conductive traces 160 may be formed via screenprinting, flexographic printing, ink-jet printing, and/or gravureprinting. Power conductors 110, 120, back power conductors 910, 920 andconductive traces 160 may include or consist essentially of a conductivematerial (e.g., an ink or a metal, metal film or other conductivematerials or the like), which may include one or more elements such assilver, gold, aluminum, chromium, copper, and/or carbon. Powerconductors 110, 120, back power conductors 910, 920 and conductivetraces 160 may have a thickness in the range of about 50 nm to about1000 μm. In some embodiments the thickness of power conductors 110, 120,back power conductors 910, 920 and conductive traces 160 may bedetermined by the current to be carried thereby. While the thickness ofone or more of power conductors 110, 120, back power conductors 910, 920and conductive traces 160 may vary, the thickness is generallysubstantially uniform along the length of the trace to simplifyprocessing. However, this is not a limitation of the present inventionand in other embodiments the thickness and/or material of powerconductors 110, 120, back power conductors 910, 920 and conductivetraces 160 may vary. In some embodiments, all or a portion of powerconductors 110, 120, back power conductors 910, 920 and conductivetraces 160 may be covered or encapsulated. In some embodiments, a layerof material, for example insulating material, may be formed over all ora portion of power conductors 110, 120, back power conductors 910, 920and conductive traces 160. Such a material may include, e.g., a sheet ofmaterial such as used for substrate 165, a printed layer, for exampleusing screen, ink jet, stencil or other printing means, a laminatedlayer, or the like. Such a printed layer may include, for example, anink, a plastic and oxide, or the like. The covering material and/or themethod by which it is applied is not a limitation of the presentinvention.

In one embodiment, the conductive traces 160 are formed with a gapbetween adjacent conductive traces 160, and LEEs 130 and CEs 140 areelectrically coupled to conductive traces 160 using conductive adhesive,e.g., an isotropically conductive adhesive and/or an ACA. FIG. 29 showsone example of a die 2720 electrically coupled to conductive traces 160using an ACA 2910. ACAs may be utilized with or without stud bumps andembodiments of the present invention are not limited by the particularmode of operation of the ACA. For example, the ACA may utilize amagnetic field rather than pressure (e.g., the ZTACH ACA available fromSunRay Scientific of Mt. Laurel, N.J., for which a magnetic field isapplied during curing in order to align magnetic conductive particles toform electrically conductive “columns” in the desired conductiondirection). Furthermore, various embodiments utilize one or more otherelectrically conductive adhesives, e.g., isotropically conductiveadhesives, non-conductive adhesives, in addition to or instead of one ormore ACAs. In other embodiments, LEEs 130 and CEs 140 may be attached toand/or electrically coupled to conductive traces 160 by other means, forexample solder, reflow solder, wave solder, wire bonding, or the like.The method by which LEEs 130 and CEs 140 are attached to conductivetraces 160 is not a limitation of the present invention.

Turning now to CE 140, in one embodiment of this invention the positionof CE 140 fits within the pitch structure of the LEEs 130. In otherwords, the placement of CE 140 generally does not change the pitch ofthe LEEs 130. For example, in FIG. 16, CE 140 does not displace theposition of any adjacent LEEs 130. In some embodiments CEs 140 may belocated between any two arbitrary LEEs 130, not just at the end orbeginning of a string 150, and the CE 140 has dimensions such that itfits between adjacent LEEs 130 spaced at the LEE pitch. For the case ofthe first exemplary embodiment described above, CE 140 would have adimension less than about 1 cm.

As discussed above, CE 140 may be one component or multiple activeand/or passive components. In one embodiment, power conductors 110, 120provide a DC voltage or substantially DC voltage and CE 140 includes orconsists essentially of a resistor 3010, e.g., a current-limitingresistor, as shown in FIG. 30A. The choice of the resistance value maybe a trade-off between a number of parameters and characteristics thatmay include, e.g., efficiency and current stability. In general, alarger resistance will result in reduced efficiency but greater currentstability, while a smaller resistance will result in increasedefficiency but reduced current stability. Variations in the current mayresult from variations in the input voltage (for example across powerconductors 110, 120), variations in forward voltage of the LEEs 130within the string, variations in the value of the current-limitingresistor, variations in current that may occur if one or more LEEs 130in the string become short-circuited or the like. In the case of CE 140including or consisting essentially of a resistor, in some embodimentsCE 140 is a discrete resistor formed within or on conductive traces 160,such as a chip resistor, a bare-die resistor or surface mount device(SMD) resistor.

As discussed above, in embodiments where CE 140 includes or consistsessentially of a resistor, there may be trade-offs between efficiencyand current stability. While such trade-offs may be acceptable incertain products, other products may require relatively better currentstability at higher efficiencies, and in these cases CE 140 may includeor consist essentially of multiple components or a circuit element, asdiscussed above. FIG. 30B shows one example of such a circuit, where CE140 includes or consists essentially of a field-effect transistor (FET)3020 and a resistor 3010. In another embodiment CE 140 includes orconsists essentially of two bipolar junction transistors (BJTs) and tworesistors.

In one embodiment, CE 140 includes or consists essentially of a FET 3020and a resistor 3010, as shown in FIG. 30B. In one embodiment, FET 3020is a depletion-mode FET that is normally on and easily allows current toflow essentially unimpeded. In order to reduce the amount of currentflowing through FET 3020, a negative voltage potential is appliedbetween its source and gate. As current begins to flow through the FET3020 and the series-connected resistor 3010, a potential differencedevelops across resistor 3010, thus generating a negative voltagepotential between the gate and source of FET 3020. Once this potentialdifference reaches a certain value equal to the pinch-off voltage of theFET 3020, the current is restricted from increasing further and thus CE140 acts as a constant-current regulator. Different FETs 3020 may bemanufactured to have different pinch-off voltage thresholds; therefore,by matching the FET characteristics to a certain value of resistor 3010,a specific current limit may be defined for CE 140

In one embodiment, the CE 140 includes or consists essentially of twoNPN BJTs 3030, 3031 and two resistors 3010, 3011 (as shown in FIG. 30C)and is connected in series with the LED string and may be located at oneend of the string or anywhere mid-string. Such a CE 140 acts like atwo-terminal polarized device, allowing current to flow only in onedirection and maintaining an essentially constant current. Thetransistor 3030 acts as a buffer that is turned on by base currentflowing through resistor 3010—changes in string voltage are thus takenup by transistor 3030. Once current starts flowing through transistor3030, base current is provided to turn on transistor 3031. Withtransistor 3031 turned on the voltage across the base-emitter junctionof transistor 3031 is nominally, e.g., 0.6V, which is the typicalvoltage drop of a standard forward biased silicon diode p-n junction.This base emitter voltage acts as a reference, so dividing that voltageby the value of resistor 3011 defines the current set point of thecircuit. It is self-correcting in the following manner. If more currenttries to flow through transistor 3030 the voltage at the base oftransistor 3031 will rise, along with the base current into transistor3031, which will increase the amount of current which may flow throughtransistor 3031. This in effect “steals” base current away fromtransistor 3030, which in turn will reduce the amount of current whichmay pass through transistor 3030. This negative feedback self-regulatesthe amount of current that may flow through the circuit. Resistor 3010preferably has a resistance value sufficiently high to limit the amountof bias current that may flow through transistor 3031 to less thanapproximately 5% of the current through resistor 3010. Thus, the totalcurrent through the LED string will be nominally, in this example, thebias current added to 0.6V divided by this resistance value. Finally, asthe voltage across the circuit changes, for example if one or more LEEsin the string short out, the voltage across transistor 3030 and resistor3010 will increase, which will slightly increase the base current intotransistor 3030, thus allowing more current to flow through transistor3030. Thus, even with the feedback response of transistor 3031 the drivecurrent may increase slightly. For example, if the voltage acrosstransistor 3030 changes by about 10 V, the current through the circuitwill increase by less than about 1 mA. The description above is of aspecific embodiment of this invention and in other embodiments thecircuit layout, elements and configuration may be different; thespecific circuit is not a limitation of the present invention.

In one example, FET 3020 is a MMBFJ113 manufactured by FairchildSemiconductor and resistor 3010 has a value of about 250 ohms to achievea constant current of approximately 5 mA. In one example BJTs 3030, 3031are MMBT2484 manufactured by Fairchild Semiconductor and resistors 3010,3011 have a value of approximately 39 kiloohms and 113 ohms,respectively, to achieve a constant current of approximately 5 mA.

In general, the efficiency and current stability increase with thenumber of components, as does the cost. In some embodiments where CE 140includes or consists essentially of multiple components, the componentsmay be in discrete form (i.e., each component individually electricallycoupled to conductive traces 160) or in hybrid form (where multipleseparate components are mounted on a submount, which is thenelectrically coupled to conductive traces 160), or in monolithic form(where multiple components are integrated on a semiconductor chip, forexample a silicon-based or other semiconductor-based integratedcircuit). In some embodiments, CE 140 may be in bare-die form, while inother embodiments CE 140 may be packaged or potted or the like. In someembodiments, CE 140 may include or consist essentially of a bare-dieintegrated circuit, for example including or consisting essentially ofresistor 3010 and FET 3020 of FIG. 30B. In some embodiments, theintegrated circuit includes or consists essentially of multiple activeand/or passive devices that are fabricated on a common semiconductorsubstrate.

In other embodiments, power conductors 110, 120 may provide AC power, orpower modulated at different frequencies and in these embodiments CEs140 may be selected accordingly or may be omitted. In one embodiment,power conductors 110, 120 may provide a standard line voltage, forexample about 120 VAC or about 240 VAC or about 277 VAC, for example atabout 50 Hz or about 60 Hz. In some embodiments, CE 140 may accommodatea plurality of input types, a so-called “universal” CE 140, while inother embodiments different CEs 140 may be required for different inputtypes. The actual component or components of CEs 140 are not limiting tothis invention; however, in preferred embodiments of this invention, thepositioning of CEs 140 does not disrupt the LEE pitch. In anotherembodiment of this invention, the positioning of CEs 140 is independentof LEE pitch.

As discussed above, CEs 140 and LEEs 130 may be electrically coupled toconductive traces 160 using a conductive adhesive. FIG. 31 shows aplan-view schematic example of a portion of a lightsheet featuring LEEs130 electrically coupled to conductive traces 160 using conductiveadhesive 2910, for example an ACA, resistors 3110 electrically coupledto conductive traces 160 using conductive adhesive 2910, and conductivetraces 160 electrically coupled to power conductors 110, 120.

FIGS. 32A, 32B, 32C, and 32D illustrate another aspect in accordancewith embodiments of the present invention. FIG. 32A is a schematic of aconductive pattern that may be used for formation of CE 140. Thestructure shown in FIG. 32A is electrically coupled to string 150 asdescribed above. Current flows through the structure from conductiveelement 160 to conductive element 160′. In some embodiments, theconductive pattern for CE 140 may permit the formation of differenttypes of CE 140. In this case one sheet design may be used for differentproducts that have different CEs 140, by placing various componentscomprising CE 140 across various conductive elements making up thestructure shown in FIG. 32A. For example, FIG. 32B shows an embodimentof the present invention where CE 140 is a resistor 3110 while FIG. 32Cshows an embodiment of the present invention where CE 140 comprises twobipolar junction transistors 3030 and 3031 and resistors 3010 and 3011.FIG. 32D shows an expanded view of FIG. 32C that includes powerconductors 110, 120 and LEEs 130. As shown, the string joins powerconductor 110 at the point identified as 3220, and the string joinspower conductor 120 at the point identified as 3230. As shown. the sameconductive trace pattern may be configured and used for multipledifferent types of CEs 140, for example comprising different numbers ofcomponents and/or different types of components. The conductive patternshown in FIG. 32A is an example of this embodiment of the presentinvention and in other embodiments other patterns or layouts may be usedto achieve the ability to use different CEs 140 with a single pattern.

While the discussion above has focused on manufacture of embodiments ofthe present invention in flexible sheet form, this is not a limitationof the present invention, and in other embodiments the inventiveconcepts may be applied to other systems. For example, some examplesabove utilize a flexible substrate 165 to permit fabrication of aflexible lightsheet and/or to permit roll-to-roll processing ormanufacture; however, this is not a limitation of the present inventionand in other embodiments substrate 165 may include or consistessentially of other materials or types of wiring boards, for exampleconventional printed circuit boards (PCBs), FR4, metal core PCBs, or thelike. For example, some examples above utilize a conductive adhesive oran ACA to attach LEE 130 to conductive elements 160; however, this isnot a limitation of the present invention and in other embodiments otherattachment methods, for example ones that may provide higher thermalconductivity or higher temperature operation, or the like, may be used.Thus, one or all of the inventive concepts of the present invention,including but not limited to (i) powering multiple strings 150 from oneset of power conductors with a constant voltage; (ii) each stringincluding CE 140 to control the current in LEEs 130 of that string;(iii) disposition of CE 140 within LEE 130 pitch; (iv) ability to cut tolength; and (v) ability to tile across the joint with substantially nochange in pitch across the joint, are applicable to any type of system.For example, FIG. 33 shows a schematic of a MCPCB including LEEs 130,where the LEEs 130 are relatively high-power packaged LEDs.

In some embodiments, a low-profile (i.e., relatively thin) lightingsystem having a relatively low weight may be desirable. For example,some applications require a relatively thin enclosure for the lightingsystem. Examples of such applications include back lighting oftranslucent panels (e.g., enclosures composed of plastic, wood, orstone), surface-mount applications where the lighting system extendsonly a small amount above the surrounding surface, flush-mountapplications where it is desirable that the lighting system consume aslittle space below the surface as possible, inlay applications where thelighting system is incorporated into another structure, back lighting offixed-image or video displays, back lighting of display or videomonitors and the like. In some embodiments it may be desirable to have alow profile in a ceiling mount application so that the lighting systemdoes not consume a large amount of space. For example, multi-storybuildings typically require a certain amount of space between floors toaccommodate electrical, heating, air conditioning and lightingfacilities. Reduction of the amount of this space may result inreduction of the cost-per-floor of the building. The use of relativelythin, low-profile lighting systems may aid in the reduction ofbetween-floor space requirements. Furthermore, houses, buildings, andother structures must be constructed to support the weight of thebuilding itself, all associated facilities, and weight added to thebuilding by its occupants as well as the occupants themselves. Ingeneral terms the weight not directly associated with the structure maybe termed the “building load.” Reducing the building load, for exampleby reducing the weight of lighting systems, potentially enables areduction in the cost of the building.

In some applications it is desirable for a lighting system to include orconsist essentially of a light sheet and a transparent or translucentpanel over the light-emitting side of the light sheet to impart one ormore optical characteristics to the lighting system and/or to protectthe light sheet. In some embodiments, it is desirable for thecombination of the light sheet and overlying panel to be relativelythin. The thickness of such a combination is determined by the thicknessof the light sheet, the thickness of the panel above the light sheet andthe spacing between the panel and the light sheet. In some embodiments,the overlying panel may act to diffuse the light, modify the lightintensity distribution, modify the light intensity distribution as afunction of angle, modify the color temperature, modify the color,modify the color temperature as a function of angle, modify theappearance of the light emitted by the lighting system, protect thelight sheet, or the like. In some embodiments, the overlying panel mayinclude or consist essentially of a flat or substantially featurelesspanel, while in other embodiments the overlying panel may include orconsist essentially of one or more optical elements or features, forexample a refractive optic, a reflector or reflective optic, a totalinternal reflection (TIR) element or optic, a Fresnel optic or element,or the like. In some embodiments, the overlying panel may include orconsist essentially of transparent or translucent words and/or images,for example for advertising, identification, signage, or the like. Thetransparency of the overlying panel is not a limitation of the presentinvention.

In one embodiment, the above-described attributes may be achieved by theuse of a very thin substrate 165. For example, in one embodiment thesubstrate 165 may include or consist essentially of a material with athickness less than approximately 200 μm, less than approximately 100μm, or less than approximately 50 μm. PET has a density of about 1.38gm/cm³, which translates to a weight per square meter of about 1.38grams per micron of thickness. Thus, one square meter of PET havingthicknesses of approximately 200 μm, approximately 100 μm, approximately50 μm, and approximately 38 μm weighs approximately 276 gm,approximately 138 gm, approximately 69 gm, and approximately 52 gmrespectively. As described herein, conductive elements, for exampleconductive elements 160 and power conductors 110, 120, may includemetals such as Cu, Al, Au, Ag, Cr, or the like or carbon or inksincluding or consisting essentially of such metals or carbon. In someembodiments, the conductive elements may have a thickness in the rangeof about 3 μm to about 100 μm, and more preferably in the range of about5 μm to about 50 μm. LEEs 130 may be attached to conductive elements 160using a variety of means, for example ACA, conductive adhesive, orsolder. The means of attachment of LEEs 130 to conductive elements 160is not a limitation of the present invention.

In some embodiments, the total lightsheet weight may be less than about1000 gm/m², less than about 500 gm/m², less than about 100 gm/m², oreven less than about 50 gm/m². For example, in one embodiment alightsheet may include or consist essentially of a PET substrate havinga thickness of about 38 μm, Cu conductive traces having a thickness ofabout 30 μm, and LEDs having a pitch of about 12 mm, the entirelightsheet having a weight of about 325 gm/m². In another embodiment, alightsheet may include or consist essentially of a PET substrate havinga thickness of about 38 μm, Al conductive traces having a thickness ofabout 9 μm, and LEDs having a pitch of about 12 mm, the entirelightsheet having a weight of about 82 gm/m². In some embodiments, therelatively thin substrate 165 may have thermal limitations; that is, thesmall thickness of the substrate 165 may render the use of conventionalsolder difficult due to the relatively high temperatures required forconventional solders. For example, conventional gold/tin (Au/Sn) soldershave a relatively high melting point, for example 80% Au/20% Sn soldershaving a composition of about 80% Au and about 20% Sn have a meltingpoint of about 280° C., which is above the melting point of PET, whichis about 265° C. Another example of a somewhat lower melting pointconventional solder is SAC 305, for example manufactured by MG Chemicalsor Kester, having a composition of about 96.5% tin, about 0.5% copperand about 3% silver, which has a melting point of about 220° C. Eventhough the melting point of SAC 305 is below the melting point of PET,it is still undesirably high. PET undergoes a crystallization reactionwhen exposed for extended times to temperatures near the glasstransition temperature (which for PET is in the range of about 67° C. toabout 81° C.), resulting in a change in properties, particularlytransparency, and thus it is often desirable to limit the thermal budget(time and temperature) for a solder-based attachment process. Lead hasbeen used in solder alloys to help achieve lower temperatures, but insome embodiments, lead may not be acceptable from a health and safetypoint of view. Bismuth (Bi) and indium (In) have been utilized asconstituents for relatively low temperature solders. In melts at about156° C. while Bi melts at about 271° C. In some embodiments, the solderincludes or consists essentially of bismuth and tin, the composition ofbismuth in the range of about 45% to about 70% and the composition oftin in the range of about 30% to about 55%. In some embodiments, thesolder includes or consists essentially of bismuth, tin, and silver, thecomposition of bismuth in the range of about 45% to about 70%, thecomposition of tin in the range of about 30% to about 55%, and thecomposition of silver in the range of about 0.1% to about 8%. In someembodiments, the solder includes or consists essentially of bismuth,tin, and silver, the composition of bismuth in the range of about 20% toabout 50%, the composition of tin in the range of about 5% to about 28%,and the composition of indium in the range of about 35% to about 65%.

Alloys of, for example, Bi, Sn, Pb, and Ag may be formulated to have aliquidus temperature in the range of, for example, about 100° C. toabout 150° C. For example, Indalloy 282 from the Indium Corporation hasa composition of about 57% Bi, about 43% Sn, and about 1% Ag and aliquidus temperature of about 140° C. Indalloy 97 from the IndiumCorporation has a composition of about 43% Bi, about 43% Pb, and about14% Bi and a liquidus temperature of about 163° C. Indalloy 281 from theIndium Corporation has a composition of about 58% Bi and about 42% Snand a liquidus temperature of about 138° C. Another even lowertemperature, but relatively more expensive, solder is InSn solder,having a composition of about 50% In and about 50% tin and a liquidustemperature about 125° C.

In some embodiments, it may be desirable to connect more than one sheettogether while still maintaining the flexibility of the sheet, forexample to have the joint region have substantially the same flexibilityas the sheet itself. Conventional methods of joining sheets, for examplesoldering adjacent sheets together, may result in the joint regionhaving a relatively higher stiffness than the sheet itself, for exampleif the solder that attaches a connecting element between two sheetsforms a rigid solder joint that may resist bending or crack underbending. FIG. 34A shows an example of one embodiment featuring a hingeor flexible member providing electrical coupling and optional compliantmechanical coupling between two lightsheets. In the embodiment shown inFIG. 34A, the lighting system includes or consists essentially of twosubstrates 165 and 165′, each including or consisting essentially ofconductive elements 160 and 160′, respectively, and a joint element 3410that electrically couples conductive elements 160 and 160′. In someembodiments, the joint element 3410 may include or consist essentiallyof metal, for example copper, brass, aluminum, gold, silver, or thelike. In some embodiments, the joint element 3410 may have a thicknessin the range of about 25 μm to about 500 μm. In some embodiments, jointelement 3410 may have a width in the range of about 0.5 mm to about 10mm; however, the width of joint element 3410 is not a limitation of thepresent invention. In some embodiments, joint element 3410 may have alength in the range of about 3 mm to about 25 mm; however, the length ofjoint element 3410 is not a limitation of the present invention.

In some embodiments, joint element 3410 may include or consistessentially of one material; however, this is not a limitation of thepresent invention, and in other embodiments joint element 3410 mayinclude or consist essentially of more than one material. For example,in some embodiments joint element 3410 may include or consistessentially of a layered structure or an alloy or compound. In someembodiments, joint element 3410 may include or consist essentially of aflat or planar conductor or conductive tape. In some embodiments, jointelement 3410 may include or consist essentially of a wire. In someembodiments, a preferred attribute of joint element 3410 is that it isflexible or compliant. In other words, in some embodiments joint element3410 is not rigid and does not impart significant stiffness to thecombined substrates 165 and 165′.

In some embodiments, the joint element 3410 may have a shape designed toprovide increased flexibility or compliance, for example as shown inFIG. 34B. FIG. 34B shows an example of a joint element 3410 featuringone or more undulations to increase the flexibility of the middle regionof joint element 3410 (for example, as an accordion fold). As shown, ajoint element 3410 having one or more undulations has a straight-linelength longer than the straight-line length between the points at whichit is anchored to substrates 165, 165′. FIG. 34C shows an example ofanother embodiment of joint element 3410. The specific shape of jointelement 3410 is not a limitation of the present invention—in someembodiments of the invention a preferred attribute is a compliant and/orflexible joint element.

While joint element 3410 has been shown as having a substantiallyconstant thickness and/or cross-section, this is not a limitation of thepresent invention, and in other embodiments the thickness and/or widthof joint element 3410 may vary within joint element 3410. For example,FIG. 34D shows an embodiment in which joint element 3410 has a thicknessin the middle region relatively less than that in the end regions, forexample to provide relatively increased flexibility in a bending region.In some embodiments, the width of joint element 3410 may also vary alongthe length of joint element 3410, for example to provide relativelyincreased flexibility in a bending region.

Joint element 3410 may be electrically and/or mechanically coupled toconductive elements 160, 160′ using a variety of means, for examplecrimping, solder, conductive adhesive, non-conductive adhesive,anisotropic conductive adhesive, or the like. The method of electricallyand/or mechanically coupling joint element 3410 to conductive traces160, 160′ is not a limitation of the present invention.

In some embodiments, joint element 3410 may provide the mechanicalcoupling or connection between substrates 165 and 165′; however, this isnot a limitation of the present invention, and in other embodimentsmechanical coupling is achieved by other means. For example, FIG. 34Eshows an embodiment featuring an additional joining member 3420 thatmechanically couples substrates 165, 165′. In some embodiments, joiningmember 3420 provides additional or substantially all of the mechanicalcoupling between substrates 165 and 165′. Joining member 3420 mayinclude or consist essentially of a variety of materials, for examplethe same material as substrate 165 or 165′, tape, or the like, forexample a semicrystalline or amorphous material, e.g., PEN, PET,polycarbonate, polyethersulfone, polyester, polyimide, polyethylene,fiberglass, FR4, MCPCB, and/or paper. In some embodiments, joiningmember 3420 may include or consist essentially of multiple layers, e.g.,a flexible material and an adhesive. For example, in some embodimentsjoining member 3420 may include or consist essentially of tape. In someembodiments, joining member 3420 may include or consist essentially of atransfer tape 3430 and a backing layer 3440, as shown in FIG. 34F. FIG.34F shows an embodiment in which the length of joining member 3420 isless than that of joint element 3410. In some embodiments, a glue oradhesive may be provided between portions of substrate 165 and 165′ ator proximate the interface therebetween.

FIG. 34E shows joining member 3420 as having a length greater than thelength of joint element 3410; however, this is not a limitation of thepresent invention, and in other embodiments joining member 3420 may havea length equal to the length of joint element 3410 or less than thelength of joint element 3410, as shown in FIG. 34F.

In some embodiments, joining element 3410 may be electrically coupled toconductive elements 160 and 160′ using solder. FIG. 34G shows an exampleof one embodiment featuring substrates 165, 165′, conductive elements160, 160′, joining element 3410, and solder 3450. In some embodiments,it may be desirable that solder 3450 does not extend along the length ofjoining element 3410 such that it forms a rigid or semi-rigid bridgebetween substrates 165 and 165′. In other words, in some embodiments aregion 3460 in FIG. 34G between the regions of solder 3450 is free orsubstantially free of solder, such that in some embodiments thestiffness or rigidity of joining element 3410 is not increased by thepresence of solder 3450 in region 3460.

In various alternative embodiments of the invention, connection of morethan one component lightsheet together while still maintaining theflexibility of the joined lightsheet may be accomplished by using arelatively small, substantially rigid electrical joint, as shown in FIG.34H. FIG. 34H depicts substrates 165, 165′ joined mechanically byjoining member 3420 and conductive traces 160, 160′ electrically coupledby a relatively small electrical connection member 3475. In someembodiments of the present invention, electrical connection member 3475may include or consist essentially of a small block of conductive metal,for example aluminum, copper, gold, silver, or the like. In someembodiments, the metal block may have a length in the range of about 2mm to about 10 mm, a width in the range of about 1 mm to about 10 mm,and a thickness in the range of about 0.1 mm to about 1 mm. In someembodiments, the conductive metal block may be attached to the powerconductors using solder, electrically conductive adhesive, electricallyconductive tape, or the like. In some embodiments, electrical connectionmember 3475 may include or consist essentially of a rigid substratebacked with electrically conductive tape, for example the rigidsubstrate may include or consist essentially of FR4, plastic, or thelike. In some embodiments, electrical connection member 3475 may includeor consist essentially of a thin conductive foil, for example aluminum,copper, gold, silver, chromium foil, or the like. In some embodiments,the conductive foil may be supported on one side by a rigid substratesuch as FR4, plastic, or the like.

In this embodiment, substrates 165, 165′ may be butted up against eachother such that there is only a small gap (if any) between substrates165, 165′ and between conductive traces 160, 160′. For example, in someembodiments, the gap may be less than 0.5 mm or less than 0.25 mm. Insome embodiments, joining member 3420 may include or consist essentiallyof an adhesive tape. In preferred embodiments, electrical connectionmember 3475 is small enough that it does not substantially change theflexibility of the lightsheet. In some embodiments of the presentinvention, the lightsheet may have a radius of curvature in a non-jointregion less than about 50 cm, or less than about 20 cm, or less thanabout 10 cm, or less than about 5 cm or less than about 1 cm. In someembodiments of the present invention, the light sheet may have a radiusof curvature in a non-joint region less than 0.5 cm. In someembodiments, the radius of curvature in the joint region may have aradius of curvature that is within ±25% of the value of the radius ofcurvature in a non-joint region, or that is within ±10% of the value ofthe radius of curvature in a non-joint region, or that is within ±5% ofthe value of the radius of curvature in a non-joint region. In someembodiments, the joint region may be a region within about 3 cm of thejoint or within about 1.5 cm of the joint, while a non-joint region maybe spaced apart from the joint by at least 1.5 cm or at least 3 cm. Inone embodiment, electrical connection member 3475 is substantially thesame size or smaller than LEE 130. In some embodiments, electricalconnection member 3475 has a dimension less than about 3 mm.

FIG. 34I depicts an expanded view of one embodiment of FIG. 34H, inwhich electrical connection member 3475 includes or consists essentiallyof a low-resistance resistor (e.g., a resistor having a maximumresistance less than about 100 milliohms, or less than about 50milliohms or less than about 20 milliohms) or “zero-ohm resistor” (or“zero-ohm link,” i.e., a low-resistance wire or jumper connection havingsubstantially the same form factor as a resistor, and typically having amaximum resistance less than about 100 milliohms, or less than about 50milliohms, or less than about 20 milliohms) that has been electricallycoupled between traces 160, 160′ using solder 3482. FIG. 34J shows anexpanded view of another embodiment of FIG. 34H, in which electricalconnection member 3475 includes or consists essentially of alow-resistance resistor or zero-ohm resistor that has been electricallycoupled between traces 160, 160′ using ACA 3484. In some embodiments,the zero-ohm resistor may include or consist essentially of a surfacemount device (SMD) resistor having a length of about 3.2 mm, a width ofabout 2.5 mm, and a thickness of about 0.55 mm and a maximum resistanceof about 50 milliohms. While the examples shown in FIGS. 34I and 34Jutilize zero-ohm resistors, this is not a limitation of the presentinvention, and in other embodiments other components that provide thedesired electrical conductivity, with the appropriate size, may also beused.

In some embodiments, one substrate 165 may overlap a second substrate165′, as shown in FIG. 34K. For example, substrates 165, 165′ may have athickness substantially equal to that of conductive traces 160, 160′,both of which are relatively thinner than electrical connection member3475. In this case there may be a small but acceptable tilt toelectrical connection member 3475 as it spans the two substrates. In oneexample, substrates 165, 165 have a thickness of about 38 μm andconductive traces 160, 160′ have a thickness of about 30 μm.

FIG. 34L is a plan view of two lightsheets joined together as describedherein. As shown, substrates 165, 165′ are adjacent to each other,either butted up against each other or overlapped. Power conductors 110,120 on substrate 165 are adjacent to power conductors 110′, 120′ onsubstrate 165′, respectively, and power conductor 120 is electricallycoupled to power conductor 120′ through electrical connection member3475, while power conductor 110 is electrically coupled to powerconductor 110′ through electrical connection member 3475′.

In some embodiments, as shown in FIG. 35, a total thickness 3510 of thelightsheet, including substrate 165, conductive traces 160, andlight-emitting elements 130, is less than about 3 mm, less than about 2mm, or even less than about 1 mm.

FIG. 36 shows an embodiment of the present invention featuring alightsheet 3650 including or consisting essentially of substrate 165 andLEEs 130 (conductive elements 160 are not shown for clarity) and anoverlying optical element 3610. Lightsheet 3650 has a thickness 3510,optical element 3610 has a thickness 3620, and a gap 3630 betweenlightsheet 3650 and optical element 3610 contributes to an overallthickness 3640 of the system. In some embodiments, overall thickness3640 may be less than about 40 mm, less than about 20 mm, less thanabout 15 mm, or even less than about 10 mm.

In general in the above discussion the arrays of semiconductor dies,light emitting elements, optics, and the like have been shown as squareor rectangular arrays; however this is not a limitation of the presentinvention and in other embodiments these elements may be formed in othertypes of arrays, for example hexagonal, triangular or any arbitraryarray. In some embodiments these elements may be grouped into differenttypes of arrays on a single substrate.

The terms and expressions employed herein are used as terms andexpressions of description and not of limitation, and there is nointention, in the use of such terms and expressions, of excluding anyequivalents of the features shown and described or portions thereof. Inaddition, having described certain embodiments of the invention, it willbe apparent to those of ordinary skill in the art that other embodimentsincorporating the concepts disclosed herein may be used withoutdeparting from the spirit and scope of the invention. Accordingly, thedescribed embodiments are to be considered in all respects as onlyillustrative and not restrictive.

What is claimed is: 1-29. (canceled)
 30. A lighting system comprising: alightsheet comprising: a substantially planar substrate; disposed on thesubstrate, (i) first and second spaced-apart power conductors eachextending in a first direction and (ii) a plurality of conductivetraces; a plurality of light-emitting strings, each light-emittingstring (i) comprising a plurality of interconnected light-emittingelements spaced along the light-emitting string, (ii) having a first endelectrically coupled to the first power conductor, (iii) having a secondend electrically coupled to the second power conductor, and (iv) beingoriented in a second direction not parallel to the first direction,wherein the power conductors supply power to each of the light-emittingstrings; and a plurality of control elements each (i) electricallyconnected to at least one light-emitting string and (ii) configured toutilize power supplied from the power conductors to control the currentto the at least one light-emitting string to which it is electricallyconnected, wherein the lightsheet is separable, via a cut spanning thefirst and second power conductors and not crossing a light-emittingstring, into two partial lightsheets each comprising (i) one or morelight-emitting strings, (ii) one or more control elements, and (iii)portions of the first and second power conductors configured to supplypower to and thereby illuminate the one or more light-emitting stringsof the partial lightsheet.
 31. The lighting system of claim 30, whereinthe weight per area of the lightsheet is less than 1000 gm/m².
 32. Thelighting system of claim 30, wherein the lightsheet is flexible.
 33. Thelighting system of claim 30, wherein a thickness of the lightsheet isless than 2 mm.
 34. The lighting system of claim 30, further comprisingan optical element disposed above and spaced apart from the lightsheet,wherein a collective thickness of the optical element and the lightsheetis less than 40 mm.
 35. The lighting system of claim 30, furthercomprising, electrically connected to the power conductors, a powersupply configured to provide a substantially constant voltage to thepower conductors.
 36. The lighting system of claim 35, furthercomprising a second lightsheet (i) coupled to the lightsheet and (ii)comprising third and fourth spaced-apart power conductors disposedthereon, wherein the power supply is configured to supply thesubstantially constant voltage to the third and fourth power conductors.37. The lighting system of claim 35, wherein the power supply isconfigured to adjust a light output of the lightsheet bypulse-width-modulating the substantially constant voltage.
 38. Thelighting system of claim 30, wherein the conductive traces comprise atleast one of copper, brass, aluminum, silver, or gold.
 39. The lightingsystem of claim 30, wherein (i) a thickness of the conductive traces isless than 50 μm, and (ii) the lightsheet comprises polyethyleneterephthalate.
 40. The lighting system of claim 30, wherein each controlelement is electrically connected to a different light-emitting string.41. The lighting system of claim 30, wherein, for each light-emittingstring, light-emitting elements thereof are spaced apart at asubstantially constant light-emitting-element pitch independent of aposition of the control element electrically connected to thelight-emitting string.
 42. The lighting system of claim 30, wherein eachlight-emitting string comprises only 12, 16, 18, or 20, 60, 72, 84, 90,96, 108, 120, 126, 140, 150, 156, 160, 168, 180, 198, 200, 204, 210, or216 light-emitting elements.
 43. The lighting system of claim 30,wherein light-emitting elements of each light-emitting string areconnected in series.
 44. The lighting system of claim 30, wherein atleast one control element is configured to provide a substantiallyconstant current to the at least one light-emitting string to which thecontrol element is connected.
 45. The lighting system of claim 30,wherein at least one light-emitting element emits substantially whitelight.
 46. The lighting system of claim 30, wherein at least onelight-emitting element comprises a bare-die light-emitting diode. 47.The lighting system of claim 30, wherein at least one light-emittingelement comprises a packaged light-emitting diode.
 48. The lightingsystem of claim 30, wherein at least one light-emitting string is afolded string having a straight-line length longer than a dimension ofthe lightsheet spanned by the power conductors.
 49. The lighting systemof claim 30, wherein, in at least one light-emitting string, eachlight-emitting element is coupled to conductive traces on the substratevia at least one of (i) a conductive adhesive, (ii) an anisotropicconductive adhesive, (iii) a wire bond, or (iv) solder.
 50. The lightingsystem of claim 30, further comprising an insulating layer disposed over(i) at least portions of some of the conductive traces, (ii) at least aportion of at least one of the first or second power conductors, (iii)at least a portion of the substrate, and/or (iv) at least portions ofsome of the light-emitting elements.
 51. The lighting system of claim50, wherein the insulating layer comprises an insulating ink.
 52. Thelighting system of claim 30, further comprising a power connector forconnecting the lightsheet to another lightsheet or to a source ofelectrical power.
 53. The lighting system of claim 30, furthercomprising a conductive joint electrically coupling two discrete regionsof the lightsheet at a joint region, a flexibility of the lightsheet atthe joint region being approximately equal to a flexibility of thelightsheet at a region spaced away from the joint region.
 54. Thelighting system of claim 53, wherein the conductive joint is flexible.